St. Louis , Missouri ( CNN ) -- Timothy G. Hendron 's co-workers were expecting him at their Missouri workplace Thursday . He arrived wearing typical office attire : Dockers and a button-down , collared shirt . But , police said Friday , Hendron also donned a fanny pack filled with magazines for the guns he allegedly used to pop off more than 100 rounds , killing three and wounding five others . Hendron arrived at work armed with hundreds of bullets and an assault rifle , two handguns and a shotgun , St. Louis Police Capt . Michael Sack said at a news conference Friday . He opened fire at about 6:30 a.m. ( 7:30 a.m . ET ) Thursday at ABB Inc. , a St. Louis transformer manufacturing company , police said . When they entered the facility , Sack said , police found `` a gruesome scene '' -- the dead and wounded and those employees desperately hiding from the shooter . The 51-year-old suspect was found inside an ABB Inc. office dead from a self-inflicted gunshot wound , police said . Carlton J. Carter , 57 ; Terry Mabry , 55 ; and Cory Wilson , 27 , were dead from gunshot wounds to the head . Mabry also was shot in a leg and Wilson was also shot in a shoulder , according to authorities . Police were investigating whether the shooter targeted the victims , Sack said . Police are also looking into the motive for the shooting , but Sack said it could remain a mystery . `` I would imagine that you could say yes [ it was premeditated ] , because most people do n't come to work armed in such a manner , but that 's just speculation , '' Sack said . `` We have to go back and try and figure out what motivated him and like I said , we may never truly know what motivated him to do this . '' Sack said police are looking into Hendron 's work history and his personal relationships . Hendron was one of a group of ABB employees listed in a lawsuit filed in 2006 against administrators of the company 's retirement plan . Police said they were working closely with ABB executives to get more information about the suspect and his status with the company prior to the incident . ABB spokesman Bob Fesmire said Thursday there are about 100 employees who work at the facility , but some of them were unable to come in Thursday because of heavy snow . Police estimated 40 to 50 employees were in the building at the time of the incident . The federal suit filed by Hendron and others accuses pension plan administrators of , among other things , causing the plan to include `` unreasonable and excessive '' fees and expenses , paid by participants , without their knowledge and not used for their benefit or that of the plan . Linda Siegfried , a spokeswoman for the law firm representing the plaintiffs , told CNN on Thursday that Hendron was among the plaintiffs , although his name is spelled three different ways in court documents . A trial on the matter is currently being held in Kansas City , Missouri , Siegfried said . She did n't know whether Hendron would have been required to be present . Online federal court records show the trial began January 5 . Siegfried would not comment further except to say the firm offers its concern for the welfare of the victims .
Timothy G. Hendron killed three people and himself at a St. Louis , Missouri , workplace Thursday . He was one of the plaintiffs in a lawsuit filed against company retirement plan administrators . Plaintiffs ' attorney : It 's unclear if Hendron was to be present at a trial in lawsuit in Kansas City . Police captain said a motive in the killings at ABB headquarters will remain a mystery .