( CNN ) -- A 25-year-old Oklahoma man was charged Friday with murder in the deaths of two girls who were found about three and a half years ago , shot to death in a ditch alongside a remote country road . `` We do n't believe that he knew ( the slain girls ) directly , '' Oklahoma State Bureau of Investigation Director Stan Florence said Friday of Kevin Sweat . `` We just believe that he happened to be in the area that day . '' According to a probable cause affidavit , Sweat told investigators on September 13 that he 'd been driving his Chevrolet Cavalier where the girls were found when he saw `` two monsters '' come at him . The suspect said he `` panicked , '' shooting the `` monsters '' first with a Glock .40 handgun and then with a .22 handgun he 'd had in his glove box , the affidavit said . It claimed Sweat had voluntarily waived his rights and agreed to talk to investigators . The `` monsters '' are believed to be best friends Taylor Paschal-Placker , 13 , of Weleetka and Skyla Jade Whittaker , 11 , of nearby Henryetta , who were discovered June 8 , 2008 , by Taylor 's grandfather . They had been shot in the head and chest , eight times for Skyla and five for Taylor , the state medical examiner reported after an autopsy . Their killings rattled Weleetka , a town of just over 1,000 residents , with police calling the shootings the community 's first murders in more than 20 years . They also set off an extensive investigation involving multiple local , state and federal law enforcement agencies and including about 650 interviews , 900 leads and 19,000 forensic tests on 800 pieces of evidence , according to Florence . In January 2010 , Sweat was among those interviewed about the girls ' murder , because he owned a Glock .40 Model 22 handgun like one of those thought to be used in the shootings . He then told an investigator then that he 'd sold such a gun in 2007 , according to the arrest affidavit . But he was not considered a suspect until this year , after being arrested and charged with the murder of his girlfriend , Ashley Taylor , Florence said . He was already in the Seminole County Jail in his girlfriend 's death when the new charges were filed , according to the state investigative bureau director . He is charged on four counts related to the 2008 case : two each of first-degree murder , plus two each of shooting with intent to kill , according to the affidavit . The witnesses cited in this document include several of Sweat 's family members , including his father , as well as the two victims ' relatives and the Glock gun company . District Attorney Max Cook , whose jurisdiction includes Creek and Okfuskee counties , said Friday that he has filed court documents requesting that Sweat be eligible for the death penalty if found guilty of murder in any of these killings . `` We feel that we are in an appropriate position to go forward in this case , '' Cook said Friday , referring to the case of the two girls . Neighbors and relatives described Taylor and Skyla as nearly inseparable , often playing together after school , riding their bikes and sleeping at each others ' houses . They were at Taylor 's house the night of June 8 , when they set off about 5 p.m. for a walk down the road . Soon thereafter , Taylor 's grandfather made a futile attempt to call her on her cell phone . He found the two girls about 30 minutes later , lying side-by-side in a ditch about a quarter-mile from the home , police said . Six weeks after the slayings , Oklahoma authorities released a 911 tape in which a breathless , nearly hysterical woman -- identified only as a family member of one of the victims -- is heard screaming , `` Somebody killed two girls . '' `` They went for a walk , and now they are both down here dead . ... My granddaughter and her friend , '' the woman said on the tape . `` Help me . Please ! '' On September 30 , a $ 5,000 reward was offered for information on `` the Glock .40 model 22 handgun used in the Weleetka girls ' homicides , '' the state investigation bureau noted on its website . A serial number was given for that weapon , one of two linked to the girls ' deaths . Ballistics tests determined that the .40-caliber shell casings found at the crime scene , matched those found on the property of Curtis Sweat , Kevin 's father , the affidavit said . Investigators determined the serial number of the gun , which had been sold to Sweat . In his September interview , the suspect admitted that he 'd purchased the Glock .40 gun in 2007 . Authorities on Friday reiterated their plea for the public 's help in tracking down this firearm , which they said Sweat may have tried to sell in March at a Tulsa gun show . Two photos of the suspect were also released : one taken around the time of the Weleetka killings and the other a mug shot after he was charged in his girlfriend 's death . `` We hope that , by releasing ( those photos ) , it will spark someone 's memory of seeing Mr . Sweat around the scene of ( Taylor and Skyla 's ) murder , '' Florence said .
NEW : Shell Oil is a major oil company with operations in the United States, Canada, and Mexico. The suspect says he saw `` two monsters '' and shot them , according to an affidavit . `` We just believe that he happened to be in the area that day , '' an investigator says . Sweat became a suspect in this case after being arrested this summer in his girlfriend 's death .