Last Wednesday, students from Great Mills High School in Southern Maryland joined a nationwide “school walkout” to call for an end to gun violence and more school safety measures. 
 
 On Tuesday morning, those same students were evacuated from their own school after gunfire rang out. 
 
 The suspected gunman, 17-year-old student Austin Wyatt Rollins, was pronounced dead hours later at a local hospital. Two teenage students were being treated for their injuries — one, Jaelynn Willey, was in critical condition — and a school resource officer who fired at the gunman was unharmed. 
 
 “This is what we train for. This is what we prepare for and this is what we pray we never have to do,” said St. Mary’s County Sheriff Tim Cameron. “And on this day we realized our worst nightmare that our greatest asset — our children — were attacked in a bastion of safety and security, one of our schools.” 
 
 The entire incident played out in less than a minute at 7:55 a.m. in a hallway at Great Mills, a school 90 miles south of Baltimore that enrolls about 1,600 students. 
 
 Cameron said Rollins fired a Glock 9-millimeter gun at a 14-year-old boy and a 16-year-old girl, who was later identified as Willey. There’s “an indication that a prior relationship existed between the shooter and the female victim,” Cameron said, an angle that investigators were pursuing Tuesday. 
 
 The school’s resource officer, Deputy First Class Blaine Gaskill, responded quickly to the scene and “engaged” the shooter, Cameron said. As Gaskill fired at Rollins, Rollins “almost simultaneously” fired his gun, Cameron said. 
 
 Investigators are still trying to determine which bullets struck which individuals. 
 
 Willey suffered life-threatening injuries and was in critical condition at the University of Maryland Prince George’s Hospital Center, while the 14-year-old boy was in good condition at MedStar St. Mary’s Hospital. 
 
 Three people were injured in a shooting at Great Mills High School in Southern Maryland on Tuesday morning, according to a county spokesman. 
 
 Officers from multiple agencies are assisting with the investigation into the shooting, which included searching a car and a home, combing through social media accounts, interviewing witnesses, reviewing footage from surveillance cameras and tracing the ownership of the gun used by the student. Cameron said there were no immediately obvious warning signs on social media before the shooting, but said investigators still needed to take a deeper look. 
 
 The St. Mary’s County Sheriff’s Office urged anyone with information about the incident to contact the FBI. 
 
 Gaskill, the school resource officer, was in uniform at the time of the incident. He’s been with the sheriff’s office for nearly six years, after four years as a correctional officer. He’s been assigned to Great Mills as a school resource officer since the start of the school year. 
 
 Cameron praised Gaskill for responding quickly to the scene. He said all his deputies have been trained in how to respond to active-shooter situations as a single officer, instead of waiting to assemble a team. 
 
 “You go to the sound of gunfire,” he said. 
 
 Deputies, the school nursing staff and others provided first aid to the three teens who were shot, including applying a tourniquet and performing CPR, Cameron said. 
 
 Senior Terrence Rhames was standing with his friends outside their first-period class when he heard a shot. He knew instantly what the loud crack meant. 
 
 He started running, heading to a first-floor bathroom before thinking, “This is a dead end.” He turned instead to sprint toward the nearest exit. Out of the corner of his eye, Rhames said, he saw a girl fall. 
 
 “I just thank God I’m safe,” said Rhames, 18. “I just want to know who did it and who got injured.” 
 
 Parents were asked to meet their children at a reunification site on the Leonardtown High School campus, where counselors and other support staff were on hand. 
 
 Lexington Park resident Shonita Somerville said she had just dropped off her 11th-grade daughter when she got a call from her saying that there was a shooting in the school. 
 
 “She was walking in the hallway and said she heard a gunshot and kids running and crying and police running in with their guns,” Somerville said. 
 
 Somerville and her daughter were reunited two hours later. 
 
 “I never thought something like this would happen here. St. Mary’s is a small little place. Now, I can say: ‘You think it wouldn’t happen? It can happen to anybody,’ ” Somerville said. 
 
 No one answered the door Tuesday afternoon at Rollins' home in Lexington Park. 
 
 Toni Foreman, who lives across the street, said she was shocked to learn that Rollins might have been involved in the shooting. 
 
 He would often walk her son, 13-year-old Ivan Foreman, home after school, and just last week, the two boys played catch, she said. "I didn't know he had any guns," she said. "He was a very good kid." 
 
 She hesitated to say she regretted letting Rollins watch her son. "I don't know what the situation was," she said. "I wish he would have reached out for help." 
 
 "He just couldn't handle the situation," whatever it was that troubled him, Ivan chimed in. 
 
 Mostly, Foreman said she felt sorrow for Rollins' family and the two victims. "My heart goes out to all the families involved," she said. "They are all victims." 
 
 The Great Mills shooting comes just over a month after a deadly rampage in a Florida high school. Seventeen people died in the Marjory Stoneman Douglas High School shooting, catalyzing a national conversation about gun violence in schools. 
 
 Last Wednesday, Great Mills students participated in the “school walkout” on the one-month anniversary of the Parkland shooting. The students called for an end to gun violence and more school safety measures. 
 
 Mikki Braley, 14, was among more than 100 Great Mills students who walked out of class last week. Those same students were evacuated from class Tuesday. “I find it crazy,” she said. “Just a week ago we were protesting against this, and now we have a shooting in our school.” 
 
 One of the student activists from Marjory Stoneman Douglas tweeted her anger about the Great Mills incident. 
 
 “Less than a WEEK ago Great Mills High School students walked out with us to protest gun violence...now they’re experiencing it for themselves,” Jaclyn Corin wrote. “The state of our country is disgusting -- I’m so sorry, Great Mills.” 
 
 Great Mills High School will be closed Wednesday, and potentially through the end of the week, said St. Mary’s County Public Schools superintendent James Scott Smith. ||||| Deputies and federal agents converge on Great Mills High School, the scene of a shooting, Tuesday morning, March 20, 2018 in Great Mills, Md. The shooting left at least three people injured including... (Associated Press) 
 
 Deputies and federal agents converge on Great Mills High School, the scene of a shooting, Tuesday morning, March 20, 2018 in Great Mills, Md. The shooting left at least three people injured including the shooter. Authorities said the situation is "contained." (AP Photo/Alex Brandon ) (Associated Press) 
 
 GREAT MILLS, Md. (AP) — The Latest on the shooting at a Maryland high school (all times local): 
 
 11:30 a.m. 
 
 A sheriff says the shooter at a Maryland high school has died after a school resource officer fired at him. 
 
 St. Mary's County Tim Cameron told a news conference Tuesday morning that the shooter and the officer both fired a round and it wasn't known if the officer's bullet killed the suspect. 
 
 Cameron says a female student and a male student were also wounded in the shooting in a hallway at Great Mills High School in southern Maryland. 
 
 ___ 
 
 10:45 a.m. 
 
 The principal at the Maryland high school where there was a shooting Tuesday morning told parents last month that the school had investigated threats of a possible shooting and found they were "not substantiated." 
 
 Great Mills High School Principal Jake Heibel told parents that school officials interviewed two students in February who were overheard mentioning a school shooting and found that they posed no threat. His letter was posted on the local news site The Bay Net. 
 
 But Heibel said the school still increased its security after social media posts about a possible school shooting "circulated quite extensively." 
 
 St. Mary's County Sheriff's spokeswoman Cpl. Julie Yingling says three people, including the shooter, were injured in Tuesday's shooting. 
 
 ___ 
 
 10:15 a.m. 
 
 A sheriff's spokeswoman says three people have been injured in a shooting at a high school in southern Maryland, including the shooter. 
 
 St. Mary's County Sheriff's spokeswoman Cpl. Julie Yingling says there have been no fatalities in the Tuesday morning shooting at Great Mills High School. 
 
 Yingling says the two victims were shot, but she doesn't know how the shooter was injured. She also didn't have the identities of the any of the three injured. 
 
 She says all three had been transported to hospitals. 
 
 ___ 
 
 10 a.m. 
 
 FBI agents are on the scene of a shooting at a high school in southern Maryland. 
 
 FBI spokesman David Fitz says the agents are there to assist the local sheriff's office and he had no immediate information about injuries or fatalities at Great Mills High School. 
 
 Agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives have also been sent to the school. 
 
 The county sheriff said deputies are on the scene and that parents or guardians should stay away, going instead to Leonardtown High School to reunite with Great Mills students there. 
 
 ___ 
 
 9:30 a.m. 
 
 A sheriff's spokeswoman says injuries have been reported after a shooting at a high school in southern Maryland. 
 
 St. Mary's County sheriff's spokeswoman Cpl. Julie Yingling says there are injuries Tuesday at Great Mills High School but she didn't know how many or the severity of the injuries. She also said she had no information about fatalities. 
 
 Agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were headed to the scene. 
 
 The county sheriff said deputies are on the scene and that parents or guardians should stay away, going instead to Leonardtown High School to reunite with Great Mills students there. 
 
 Maryland Gov. Larry Hogan and Rep. Steny Hoyer tweeted that they're monitoring reports and urged people to follow the instructions of local law enforcement at the scene. 
 
 ___ 
 
 9:10 a.m. 
 
 School officials report that there's been a shooting at a Maryland high school, that the 'event is contained' and the campus is on lockdown. 
 
 Federal agents from the bureau of Alcohol, Tobacco and Firearms are going to the scene, their agency tweeted. 
 
 The St. Mary's County Public Schools said on its website early Tuesday that there was a shooting at Great Mills High School, located in the southern end of the state. 
 
 The county sheriff said deputies are on the scene, and that parents or guardians should stay away, going instead to Leonardtown High School to reunite with Great Mills students there. 
 
 Maryland Gov. Larry Hogan and Rep. Steny Hoyer tweeted that they're monitoring reports and urged people to follow the instructions of local law enforcement at the scene. ||||| CLOSE A Maryland Sheriff says the gunman at Great Mills High School is dead after he shot two students and a school resource officer fired at him. Sheriff Tim Cameron said a female student and male student were also injured. (March 20) AP 
 
 Emergency responders are at Great Mills High School in Lexington Park, MD after a shooting at the school, March 20, 2018. (Photo: JIM WATSON/AFP/Getty Images) 
 
 A student gunman opened fire Tuesday at a high school in southern Maryland, injuring two students before an armed school resources officer intervened, authorities said. 
 
 The gunman, identified as Austin Wyatt Rollins, 17, was killed, but St. Mary's County Sheriff Tim Cameron said it was not immediately clear whether the school officer fired the fatal shot or whether the gunman killed himself. 
 
 The attack began shortly before classes were scheduled to start at Great Mills High, a 1,500-student school 65 miles south of Washington, D.C. Cameron said Rollins was armed with a Glock, semiautomatic handgun when he shot a 16-year-old female student in a hallway. A 14-year-old male student also was shot. 
 
 "Our school resource officer was alerted to the events," Cameron said. "He engaged the shooter and fired a round; subsequently the shooter fired a round as well." 
 
 Cameron said it was not clear whether the gunman shot himself or fired at the resource officer, identified as Deputy First Class Blaine Gaskill. 
 
 The female student was hospitalized in critical condition, and the male student was in stable condition, Cameron said. Gaskill, who was not injured, followed protocol, Cameron added. 
 
 "This is what we prepare for, this is what we pray we will never have to do," Cameron said. "The notion that this can't happen here is no longer a notion." 
 
 More: 'We deserve better': Students nationwide walk out 
 
 More: Nikolas Cruz's brother arrested at Marjory Stoneman Douglas High 
 
 Cameron said the shooter and the female victim had a prior relationship. Authorities were reviewing social media posts to "piece together" a possible motive for the shooting, he said. He asked that no one jump to conclusions until the investigation is concluded. 
 
 "We are a very tight-knit community," Cameron said. "So now what I would ask our community to do is pray for the victims." 
 
 The shooting took place less than a week after some Great Mills students joined tens of thousands of students across the nation in a walkout to protest gun violence. The walkout was spearheaded by survivors of the Valentine's Day rampage at Marjory Stoneman Douglas High School in Parkland, Fla., that killed 17 students and faculty. 
 
 Parkland teens expressed solidarity Tuesday with the students at Great Mills on Twitter. 
 
 "Less than a WEEK ago Great Mills High School students walked out with us to protest gun violence...now they’re experiencing it for themselves," tweeted Jaclyn Corin. "The state of our country is disgusting - I’m so sorry, Great Mills." 
 
 Tweeted Emma González: "We are Here for you, students of Great Mills together we can stop this from ever happening again." 
 
 The shooting also took place less than a month after Great Mills High School Principal Jake Heibel told parents that officials had investigated threats of a possible shooting. Law enforcement was contacted, and the threat was "not validated," Heibel told parents. 
 
 On Tuesday, the school was placed on lockdown immediately following the shooting. "There has been a shooting at Great Mills High School," the school district said in a statement on its website. "The school is on lockdown (and) the event is contained. The Sheriff's office is on the scene, additional information to follow." 
 
 Dozens of law enforcement vehicles surrounded the school on a cold, rainy day. The St. Mary's County Sheriff's Office urged parents to gather at another school in the county to reunite with their children. 
 
 The Bureau of Alcohol, Tobacco and Firearms said special agents from Baltimore and Hyattsville joined the investigation. Gov. Larry Hogan said state police were ready to provide support and that his office was monitoring the situation. "Our prayers are with students, school personnel and first responders," he said. 
 
 Jill Morris, president of the county education association, called the shooting "devastating" for the school's students. 
 
 "We are resolved to provide all the support and comfort we can to our colleagues and neighbors ... while we work together toward a day when no school community ever has to experience this type of tragedy," she said. 
 
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– The latest school shooting has left two students wounded and the gunman dead at Great Mills High School in Maryland's St. Mary's County, reports the Baltimore Sun. The shooting happened about 8am, and details are beginning to emerge: Sheriff Tim Cameron says a male student fired at a female student in a hallway, and he apparently struck her and a male student nearby, reports USA Today. A school resource officer arrived on the scene and fired at the shooter, says the sheriff, and "that stopped any further attack or assault." The unidentified gunman is dead, says Cameron, but it was not immediately clear whether it was the shots fired by the school resource officer that killed him, per the AP. The Sun lists the 14-year-old boy as being in good condition; the 16-year-old girl was said to be hospitalized in critical condition but has been stabilized. FBI agents were on the scene to assist deputies. No word yet on a possible motive.