NBC 5 Investigates has new information on explosives found in Micah Xavier Johnson's home and weapons discovered at the scene.
Law enforcement sources with knowledge of the investigation say authorities found what are called binary explosives at Johnson's home.
These materials are sold in pre-packaged kits and are used by shooting enthusiasts to create explosive targets for shooting practice.
In large quantities, they can cause a significant blast.
The explosives were discovered Friday in search of Johnson's home in Mesquite.
At a news conference Monday, Dallas Police Chief David Brown also described what he called a large stockpile of bomb making materials.
"He knew what he was doing. He wasn't a novice. We're trying to determine how he knew all of that," said Brown.
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Investigators are still trying to determine if anyone else helped Johnson or if he learned bomb-making skills on his own online.
At the crime scene, a team of 70 FBI evidence technicians is wading through a sea of shell casings from guns fired by Johnson and police officers returning fire.
Monday, sources with knowledge of the investigation said in addition to a military-style rifle, Johnson carried a .25-caliber semi-automatic pistol and a 9 mm semi-automatic pistol.
The weapons were fired using what's known as a shoot-and move-technique designed to keep police off guard.
"Once he moves to another position those officers now have to reacquire him and readjust their aim and put active fire to eliminate the threat. Their decision making process was interrupted by his movement," said former FBI agent Gregory Shaffer.
In an interview with TheBlaze, father James Johnson says the family had no warning.
"I didn't see it coming. I love my son with all my heart. I hate what he did," James Johnson said.
Police vow to find out if anyone else might have known, or might have helped.
"We're going to turn over every rock and we're going to follow every lead until I'm satisfied," Brown said.
It's still not clear to police what Johnson planned to do with the bomb-making materials in his home.
So far police have not found any devices at the scene of Thursday's attack even though Johnson told police he had planted improvised explosive devices when he spoke to police negotiators.
