Dallas - Military service changed the Dallas gunman from an extrovert into a hermit, his parents said in an excerpt of an interview published on Monday.Micah Johnson's mother, Delphine Johnson, told The Blaze website in an interview published on Monday that her son wanted to be a police officer as a child and that his six years in the Army Reserve, including a tour in Afghanistan, were "not what Micah thought it would be ... what he thought the military represented, it just didn't live up to his expectations".His father, James Johnson said haltingly and through tears: "I don't know what to say to anybody to make anything better. I didn't see it coming."Micah Johnson, a black 25-year-old, fatally shot five officers in Thursday's attack, which happened while hundreds of people were gathered in downtown Dallas to protest recent fatal police shootings, and wounded at least nine officers and two civilians. Authorities have said he had plans for a larger assault, possessed enough explosive material to inflict far greater harm and kept a journal of combat tactics."We're convinced that this suspect had other plans and thought that what he was doing was righteous and believed that he was going to target law enforcement - make us pay for what he sees as law enforcement's efforts to punish people of color," Dallas Police Chief David Brown told CNN's State of the Union on Sunday.The fact that Johnson had material for explosives and talked of using homemade bombs during a stand-off with police before he was killed indicated he could have inflicted more damage with more time, Dallas County Judge Clay Jenkins said.Crime of opportunity"If this had not been a crime of opportunity where the protest was quickly organised in response to events in the same week ... he could have caused a lot more harm than he did," Jenkins said.Brown also revealed details about Johnson's negotiations with police, saying he laughed at authorities, sang and at one point asking how many officers he had shot. Johnson insisted on speaking with a black negotiator and wrote in blood on the wall of a parking garage where police cornered and later killed him, Brown said.The gunman wrote the letters "RB" and other markings, but the meaning was unclear. Investigators are trying to decipher the writing by looking through evidence from Johnson's suburban Dallas home, Brown said.The writing suggested that Johnson was wounded in a shoot-out with police. An autopsy will confirm exactly how many times he was hit, Jenkins said.The police chief defended the decision to kill Johnson with a bomb delivered by remote-controlled robot, saying negotiations went nowhere and that officers could not approach him without putting themselves in danger. He also said he became increasingly concerned that "at a split second, he would charge us and take out many more before we would kill him".The shootings just a few blocks from where President John F Kennedy was slain in 1963 marked the deadliest day for US law enforcement since the September 11, 2001, terrorist attacks.Origins of weapons Federal agents are trying to trace the origin of the weapons used, including a military-style semi-automatic rifle. About 30 agents are involved in identifying bullet casings, said William Temple, the Dallas agent in charge for the Bureau of Alcohol, Tobacco, Firearms and Explosives.The large crime scene includes the parking garage where Johnson was killed and at least two other sites where he is believed to have fired at officers.The attack began on Thursday evening during protests over the police killings of Philando Castile, who was fatally shot near St Paul, Minnesota, and Alton Sterling, who was shot in Baton Rouge, Louisiana, after being pinned to the pavement by two white officers.Video from Dallas showed protesters marching along a downtown street about 1km from City Hall when shots erupted and the crowd scattered, seeking cover.