Few details have yet to emerge about the suspect in the aftermath of the worst attack against US law enforcement since 9/11.
The 25-year-old was killed when police detonated a bomb, set on a robotic device, after a stand-off between Johnson and police which lasted for hours.
The army veteran was reportedly “upset” about two black men who had been killed earlier in the week by police, and he told police he wanted to “kill white people”.
According to an army official, Johnson was a private first class in the US army who spent a year between 2013 and 2014 in Afghanistan, serving a total of about six years in the military.
There have been reports that he was “reclusive” but was spotted a few times in the local post office. He lived with his mother in a suburban area outside of Dallas.
Helicopter footage has shown Ms Johnson’s home in Mesquite, east of Dallas. He has other family members who live in Mesquite, according to reports.
The shooter told police that he was “not affiliated with any groups” and carried out the attack “alone”, according to Dallas Police Chief David Brown.
He also told authorities that "the end was coming".
“This was a well-planned, well-thought out and evil attack,” said Mr Brown, who is still searching for other suspects.
The Los Angeles Times reported that Johnson had no criminal history and no ties to terror groups.
The car he drove to the attack was a black SUV, which belonged to his mother, Delphene Johnson.
He reportedly was carrying so much ammunition that it was falling out of his pockets, and he used an AR-15 rifle, similar to other mass shootings in recent US history.