Micah Johnson was planning a larger attack in Dallas, a law enforcement source has said

The gunman who killed five cops in Dallas was planning a larger attack but launched his assault early because the protest was too good an opportunity to miss, a police source said.

Veteran Micah Johnson went on the rampage with an AR-15 assault rifle and handgun on Thursday night, but left explosive material at home.

A law enforcement source told WFAA that Johnson was 'planning something bigger' but cut preparations short because he knew scores of police officers would man the Black Lives Matter protest.

Detectives found bomb making materials, ballistic vests, rifles, ammunition and a personal journal of combat tactics at Johnson's mother's home in Mesquite, Texas, the day after his horrific spree.

'We think he was probably planning something bigger based on what we found at the house with the explosive materials,' the police source said.

'He had a bunch of explosive materials. He didn’t have the explosives created.'

Johnson's plan was 'to kill as many as he could', the source said, but he could have killed more if he had longer to prepare his attack.

'I think that target of opportunity is what drove him as far as timing,' the source said.

'He literally had hundreds and hundreds of rounds in magazines attached to his body so it wasn’t like he was running out of ammunition.

'He definitely was ready to go and intending to inflict more damage. His plan was to kill as many as he could.'

Detectives found bomb making materials, ballistic vests, rifles, ammunition and a personal journal of combat tactics at Johnson's mother's home in Mesquite, Texas, the day after his horrific spree

Johnson (pictured shooting a police officer) shot 14 people during his cop-killing spree in downtown Dallas. Of those, 12 were police officers

Johnson carried an AR-15 assault rifle (similar model pictured above) and a handgun during the shooting

Johnson shot 14 people during his cop-killing spree in downtown Dallas. Of those, 12 were police officers. Five cops - Patrick Zamarripa, Michael Krol, Lorne Ahrens and Michael J. Smith, as well as DART Officer Brent Thompson - died.

Officers from the Bureau of Alcohol Tobacco and Firearms took evidence boxes out of the house after finding rifles, ammunition and explosive material, as well as different lengths of pipe.

Cops cornered Johnson at El Centro College at around 11pm on Thursday and attempted to negotiate, but four hours later the talks failed and a robot was brought in to detonate a bomb and kill the suspect.

He claimed he had planted bombs all over the city but this turned out to be an empty threat.

Johnson wore body armor, which would explain why a cop was not able to kill him when he confronted him in a one-on-one situation which was caught on camera. It resulted in the cop being executed.

The shooter fired from an 'elevated position', picking off officers 'ambush style,' police said, adding that he shot some of the cops in the back.

The casualties include Dallas police officers Patrick Zamarripa (center), Michael Krol (right), Lorne Ahrens and Michael J. Smith, as well as DART Officer Brent Thompson (left)

Fallen Dallas, Texas police officer Lorne Ahrens pictured on the left. On the right, murdered Dallas officer Michael J Smith

Johnson reportedly used military skills he picked up while serving in the Army, which saw him sent on one tour of Afghanistan.

He also trained at a private self-defense school that teaches special tactics, including 'shooting on the move', a maneuver in which an attacker fires and changes position before firing again.

The Academy of Combative Warrior Arts refers to one of its courses as a 'tactical applications program'.

Johnson appears to have been inspired by black militant groups on Facebook and 'liked' a number of pages speaking of revolution.

He posted a rant about lynching on one such page and also followed Richard Griffin, aka Professor Griff from the hip-hop group Public Enemy, who embraces a radical form of Afrocentrism and has written a book called A Warrior's Tapestry.

It has also emerged that Johnson worked for a social services group called Touch of Kindness, which provides care for people with disabilities.