Military service changed suspected Dallas gunman Micah Johnson from an extrovert into a hermit, his parents have said.
Johnson's mother, Delphine Johnson, said in an interview that her son had 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 also told The Blaze website: "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, is suspected of fatally shooting five officers in Thursday's attack.
He also wounded at least nine other officers and two civilians before he was killed.
The incident happened while hundreds of people were gathered in Dallas to protest against recent fatal police shootings.
Authorities have said Johnson 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 colour," Dallas Police Chief David Brown told CNN.
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.
He added: "If this had not been a crime of opportunity where the protest was quickly organized in response to events in the same week ... he could have caused a lot more harm than he did."
Mr 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.
The gunman wrote the letters "RB" and other markings, but the meaning is unclear. Investigators are trying to decipher the writing by looking through evidence from Johnson's suburban Dallas home.
The writing suggested that Johnson was wounded in a shootout with police.
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 became increasingly concerned that "at a split-second, he would charge us and take out many more before we would kill him".
The shootings took place just a few blocks from where president John F Kennedy was slain in 1963.
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.
The wider 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 street about half a mile from City Hall when shots erupted and the crowd scattered, seeking cover.
Among those injured were two officers from El Centro College, identified them as Cpl Bryan Shaw and Officer John Abbott.
Cpl Shaw was struck by a bullet as he guarded an entrance to the college, but treated on scene, the statement said.
Officer Abbott was also guarding the entrance, and was hurt in both legs from flying glass after it was struck by bullets.
Cpl Abbott tended to his wounds at the scene and then returned to assist others, the statement said.
Dallas police previously said seven officers and two civilians were hurt in the attack, but its number of wounded did not include any El Centro College officers.