The Dallas police chief says the suspect in the deadly attack on officers taunted authorities during two hours of negotiations, laughing at them and at one point asking how many officers he had shot.

The chief and the county's most senior elected official also said Sunday that Micah Johnson had larger attack plans and possessed enough explosive material to inflict far greater harm.

Dallas Police Chief David Brown says Johnson, a black Army veteran, insisted on speaking with a black negotiator. The chief says he also wrote in blood on the wall of a parking garage where police cornered and later killed him.

The shootings marked the deadliest day for U.S. law enforcement since the Sept. 11, 2001, terrorist attacks. Five officers were fatally shot just a few blocks from where President John F. Kennedy was slain in 1963.