At one point the Dallas police chief asserted that four attackers were working together with rifles and triangulating themselves in positions for the attack. Two of them were reported as snipers on roof. This led me to estimate that this was probably some team-trained (supremacist) militia trying to instigate a civil war.

Current status is that one man alone was responsible. An army veteran who was, according to this video, trained in infantry combat. Three other persons are in custody but possibly not related to the incident.

What explain the far diverging situation reports by the Dallas Chief?

The single identified shooter was eventually trapped and the police negotiated with him. Negotiations broke off, according to the police, and the police used a remote controlled "robot" to deliver a bomb next to the trapped shooter where it was then exploded. The suspect was killed by the explosion.

This is the very first known use of a remote controlled vehicle based improvised explosive device, or RC-VBIED in military speak, by a civil police force. The vehicle was a remote controlled device on rubber tracks as they are often used to examine and explode suspicious packages.

The suspected shooter had been surrounded and trapped for some time.

Was the suspect still an imminent danger?