Furthermore, police are now looking for clues to understand the meaning of the letters "RB", written by Johnson in blood (from his wounds) on a garage wall, where the suspect had held under siege by officers for almost five hours.
Police also found evidence of bomb-making material "large enough to have devastating effects throughout" Texas and a journal full of "ramblings" during a search of the suspect's home in Mesquite, according to Brown.
Before he was killed in a standoff with police Johnson reportedly said he wanted to kill white people especially white police officers, after a string of police shootings of black men in USA cities.
During the interview, Brown added that there were indications Johnson was planning more wide-spread attacks, saying, "We're convinced this suspect had other plans and thought that what he was doing was righteous".
The parents of Micah Johnson, the gunman who killed five police officers in Dallas last week, have spoken out for the first time since the attack.
The deaths of two black men in police shootings last week, Alton Sterling, 37, in Louisiana and Philando Castile, 32, in Minnesota, caused Johnson to bring forward his attack.
"I approved it and would do it again if presented with same circumstances", Brown told CNN on Sunday, referring to the strategy of deploying a bomb-equipped robot into a room where the suspect was holed up after his shooting rampage.
During the vigil on Monday night, which was also attended by police officials, relatives and friends of the killed people, Dallas Police Association President Ron Pinkston read out the names of all the fallen officers, Xinhua news agency reported. "This wasn't some novice", Brown said.
The details made for significant new disclosures about the killings that have rocked the Dallas community and the nation.
The police asked media to stop all live feeds around headquarters "for the safety of our officers", the BBC's James Cook reports. It was not clear from Brown's comments if police obliged this request.
Funeral services for Sergeant Michael Smith of the Dallas Police Department are planned for Thursday.
The Dallas police chief said authorities have not ruled out if others were, in his words, "complicit" in the shooting rampage. The police said on Saturday they had no choice but to take out Johnson remotely after their efforts to talk him into surrendering ended unsuccessfully. A robot-delivered bomb ultimately killed Johnson after a standoff.