OMAHA , Nebraska ( CNN ) -- Investigators probing the deadly mall shooting in Omaha have seized computers and are analyzing information on Web sites in the search for clues in the case , police said Thursday . The 19-year-old gunman sent at least one text message to his former girlfriend , with whom he broke up about two weeks ago , Omaha Police Chief Thomas Warren said . Robert Hawkins also left a voice mail for his mother before killing eight people at a department store Wednesday . He chose his victims randomly , police believe , then took his own life . Hawkins visited a friend near the Westroads Mall before the shootings and apparently went directly to the shopping center after that meeting , Warren said . Police do n't yet know why Hawkins chose the mall or the Von Maur department store in particular , Warren said , adding only that the teen `` may have frequented the Westroads Mall . '' See who Hawkins killed in department store » . The incident itself appeared to be premeditated , as Hawkins left a suicide note and other correspondence , Warren said . Watch officials detail the rampage » . `` Typically there are hints that something like this may take place , '' Warren said . `` Certainly you ca n't anticipate someone engaging in this type of shooter rampage , but if there is any justification , any explanation , '' police will find it , he said . `` Apparently he had been experiencing some mental health problems , ideations of suicide . '' Debora Maruca-Kovac -- a friend of Hawkins ' family who was letting him live in her home -- found the suicide note just minutes before the shootings . Watch her describe their last conversation » . `` He basically said how sorry he was for everything , '' she told CNN 's Anderson Cooper on Wednesday . `` He did n't want to be a burden to people and that he was a piece of s -- - all of his life and that now he 'd be famous . '' Warren said the rifle used was an AK-47 . Police have n't finished tracing the gun , but believe Hawkins stole it from his stepfather 's home . Security officers flagged Hawkins as suspicious when he entered the mall . He left soon after he entered , then returned less than six minutes later with something apparently hidden in a balled-up sweatshirt . He went up an elevator to the mall 's third floor , then immediately began firing , ultimately turning the firearm on himself , Warren said . `` It does n't appear as though there was an opportunity for intervention , '' Warren said . Hawkins fired more than 30 rounds , the police chief said . The shootings sent panicked holiday shoppers fleeing for cover . `` It was just so loud , and then it was silence , '' said witness Jennifer Kramer , who hid inside a circular clothing rack . `` I was scared to death he 'd be walking around looking for someone else . '' Watch how Kramer and her mother hid » . A friend of Hawkins ' said he had n't thought Hawkins was capable of such violence . `` He was the one guy , you know , if people would be getting in a fight he 'd be trying to break it up , '' said Shawn Saunders , who had known Hawkins for about 2½ years . `` If there were arguments amongst our friends or groups , he was kind of like the calm , cool and collected one . '' Watch how Saunders learned Hawkins was the shooter » . Nebraska Gov . Dave Heineman said Hawkins had been a ward of the state for nearly four years , but he did not specify in what capacity . The state 's custody ended in August of last year , Heineman said . U.S. Army recruiters turned Hawkins down last summer when he tried to enlist , a source familiar with the situation said Thursday . The source did n't want to be named because it is against the military 's rules to discuss potential recruits . The reason for his rejection was unclear . Heineman ordered that flags throughout the state be lowered to half-staff through Sunday . The dead include six store employees and two customers , ranging in age from 24 to 66 . One store employee was in critical but stable condition Thursday and another had been upgraded from critical to serious , according to hospital officials . Another person was still being treated Thursday afternoon , Warren said , but he did not specify whether the individual was a customer or employee . Two other customers had been treated and released , he said . Westroads Mall remained closed Thursday , but the facility , including the Von Maur store , could reopen Friday . E-mail to a friend . CNN 's Kevin Bohn contributed to this report .
Police search computers , examine information on Web sites . Gunman may have targeted the Westroads Mall , police say . Mall shooter was ward of state for almost four years , police says . Police recruiters turned down David Hawkins when he tried to volunteer .