Dallas gunman Micah Johnson wrote a message in blood on the walls close to where he was killed and laughed and sang songs during negotiations, the city's police chief has revealed.
David Brown told CNN that Johnson wrote the letters "RB" near to where he was eventually blown up by police and officers were still trying to decipher what the message stood for.
In defending his decision to detonate an explosive-laden robot to end the stand-off, Brown also painted a disturbing picture of the gunman, saying he was "playing games" during negotiations and was determined to kill as many officers as he could.
"He lied to us, was playing games and laughing and singing at us, asking how many did he get and he wanted to kill some more," he said.
"There was no progress on negotiation and I began to feel on a split second that he would charge us and take out many more before we killed him."
Brown said he could not recall what songs Johnson was singing but added that he seemed "very much in control and very determined".
The police chief also said he was convinced that Johnson had already planned to launch an attack, but decided to bring his plans forward following the police shootings of Alton Sterling and Philando Castile last week.
"I am convinced that he had other plans and thought what he was doing was righteous and that he was going to make us pay," he said.
"We believe the deaths in Louisiana and Minnesota just sparked his delusion."
Officers are still trawling through a "rambling" journal retrieved from Johnson's home.
Brown, whose own son, David Brown Jr, was killed in 2010 after he shot and killed a policeman, also issued a message of conciliation to other protesters against police violence across the country.
"We are sworn to protect you and your right to protest and we will give our lives for it," he said. "The law-enforcement community is grieving. Words matter and we need to know that you appreciate what we are doing for this country."
On Saturday, it emerged that Johnson had practised military-style drills in his front garden and trained at a private self-defence school that teaches special tactics, including 'shooting on the move', in which an attacker fires and changes position before firing again.
Johnson, an army veteran who had served in Afghanistan, received instruction at the Academy of Combative Warrior Arts in the Dallas suburb of Richardson about two years ago, said Justin J Everman, the school's founder and chief instructor.
Mr Everman's statement was corroborated by a police report from May 8, 2015, when someone at a business a short distance away called in a report of several suspicious people in a parked SUV.
The investigating officer spoke to Johnson, who said he "had just gotten out of a class at a nearby self-defence school".
Dallas was gripped by a new security scare on Saturday night, triggered by an anonymous threat.
Swat teams deployed around the Dallas Police Department headquarters while officers investigated reports of a suspicious person in a parking garage.
They finally gave the all-clear around two hours later.
Police took "precautionary" security measures across the city after receiving "an anonymous threat against law enforcement", the police said.
The scare came as another night of marches against police brutality was under way in several US cities, a groundswell of protest that shows little sign of abating.
Protesters led by the 'Black Lives Matter' movement are demanding justice for two African-Americans shot dead by police this week - their dying moments captured in viral video footage that stunned the nation. (© Daily Telegraph, London)