Investigators in Texas reportedly believe that the sniper who shot and killed five Dallas police officers Thursday had legally purchased the weapons he used in the massacre either on the Internet or at a gun show.

A law enforcement official told The Wall Street Journal on Monday that Micah Johnson used an Izhmash-Saiga 5.45 mm high-powered rifle in the attack. The weapon is a variation of an AK-style military weapon.

The official said that Johnson was also carrying a Glock 9mm semiautomatic pistol and a .25-caliber semiautomatic pistol. However, it was unclear whether he had fired them in the attack.

Dallas police said Friday that during a search of Johnson’s home, detectives found bomb making materials, ballistic vests, additional rifles, ammunition and a personal journal of combat tactics.

According to The Journal, officials recovered 1 pound of Tannerite, a powder marketed to make exploding targets for shooting practice, and a can of acetone, that could be mixed with other material to make explosives.

The official said it was unclear when the purchases were made and that there were no restrictions that would’ve barred Johnson from buying guns legally. The official told the paper that Johnson was very active on several gun websites and discussed them in different online chat rooms.

Investigators believe that Johnson originally planned a much larger attack. Law enforcement source told WFAA-TV over the weekend that the Army veteran changed his attack plan so the shootings would coincide with the police protests over the recent killings of African-American men at the hands of officers.

“He knew what he was doing. This wasn’t some novice,” Dallas police Chief David Brown said Monday, referring to the explosives that were found in the home Johnson shared with his mother.

On Saturday, the Associated Press reported that Johnson received training from a private self-defense school that teaches firearm tactics, including "shooting on the move."

A person who said he was in charge of the organization told AP that Johnson received instruction at the Academy of Combative Warrior Arts in the Dallas suburb of Richardson about two years ago. The man refused to answer additional questions and would not give his name.

The academy website refers to one of its courses as a "tactical applications program," or TAP.

"Reality is highly dynamic, you will be drawing your firearm, moving, shooting on the move, fixing malfunctions, etc. all under high levels of stress," the website says. "Most people never get to train these skills as they are not typically allowed on the static gun range."

The TAP training includes "shooting from different positions," ''drawing under stress" and "drawing from concealment."

Brown said that investigators are going through more than 170 hours of body camera and dashboard footage taken by police during the killings.

Brown on Monday urged protesters – specifically young black men – to join his force to help improve relations with minority communities.

“Become part of the solution. Serve your community,” Brown said. “We’re hiring. Get off that protest line and get an application in. We’ll put you in your neighborhood and we will help you resolve some of the problems you’re protesting about.”

President Barack Obama will be in Dallas on Tuesday as the Dallas Police Department began preparing funeral arrangements for the fallen officers.

The Associated Press contributed to this report.

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