SYCAMORE -- The mother of shooting victim Thomas Kosta filed a lawsuit on Friday against Sycamore police officer Rob Rosenberg and his 17-year-old son, Steven, seeking more than $350,000 in damages. Jacquelyn Kosta, who was appointed the administrator of Thomas' estate in June, claims negligence on the part of the Rosenbergs for the events leading up to Thomas' death inside the Rosenberg home on May 11. In part, the suit states that the Rosenbergs "carelessly and negligently failed to keep (a) handgun and live ammunition under lock and key when the defendant knew, or in the exercise of ordinary care, should have known that (Steven) was aware of the presence of (a) handgun and live ammunition. "As a direct and proximate result of the aforesaid wrongful acts ... (Thomas Kosta) was fatally injured when the defendant's son, Steven Rosenberg, discharged the handgun striking (Kosta) in the chest." While both Rosenbergs are listed on three different counts of negligence, Steven is listed separately for firing a bullet "from a pistol he was playing with." The gun used in the shooting was Rob Rosenberg's service weapon. The Sycamore Police Department took unspecified disciplinary action against Rosenberg, who is on vacation and not available for comment. Steve Rosenberg pleaded guilty in juvenile court to involuntary manslaughter July 11 and received an "indeterminate sentence," meaning officials with the Illinois Department of Corrections will determine the appropriate time for his release. At most, he could remain in an Illinois youth center until his 21st birthday. By way of his guilty plea, Rosenberg admitted to firing a fatal shot from his father's service weapon while he, Kosta and another friend were in the residence in the Edgebrook Mobile Home Park. According to testimony in criminal hearings, Rosenberg believed there were no bullets in the gun when he pointed it at Kosta and pulled the trigger. The bullet went through Kosta's arm and struck his heart. The Kosta family attorney, Terence Mahoney, did not immediately return a phone call Monday afternoon.