Police and crisis negotiators converged on the parking lot of the Aberdeen Walmart Thursday night after receiving a report of a man in a vehicle with a gun who was threatening to harm himself.After lengthy attempts at negotiating that received no response, police moved in on the vehicle and found the occupant, age 29, was already dead.The incident began when the Harford County Sheriff's Office received a mobile phone call from that came from a man, who said he lived in the Edgewood area and was threatening to kill himself with a handgun, Aberdeen Police Department spokesperson Det. Sgt. Will Reiber said."The vehicle was located in the Walmart parking lot, which is how we [Aberdeen Police] got involved," Reiber said.Aberdeen Police officers responded to the Walmart, in the 600 block of Philadelphia Boulevard, at 7:50 p.m. Thursday and quickly located the vehicle."They tried to create a dialogue, but the man did not respond," Reiber said.Because officers had been notified the man was armed with a handgun and thus posed a potential threat to the safety of store patrons and others in the area, a perimeter was set up around the vehicle and the Harford County Crisis Negotiation Team was called, Reiber said.Additional attempts by negotiators to establish communication with the individual were not successful, Reiber said, and the Harford County Municipal SWAT team members approached the vehicle. They determined from looking from outside the vehicle that the man inside had sustained head trauma.Reiber said the officers gave immediate medical attention but the man was already deceased.Crime scene investigators determined the man sustained a single self-inflicted gunshot wound. His body was transported to the Office of the State Medical Examiner for further examination, police said.