Due to the nature of the deliberate and premeditated attack on law enforcement officers in Dallas, the resulting death of the sniper by bomb was inevitable. The only other option was an attempt at a kill shot to the head thru automobile glass which may or may not have succeeded. Had the person not been wearing body armor the results may have been very different.
The Dallas police had a right to use a bomb to kill the shooter. The shooter clearly intended to kill more police officers, and it is unclear if he would have been taken alive. The police were justified in killing him. Whether they used a bomb, a gun, a knife, or some other means is immaterial to the matter.
No, the police were in the wrong to use a bomb to kill the sniper. I believe that using explosive devices in order to stop a specified target in a major city can have disastrous effects. There is a potential for additional casualties and/or injuries to others around the main target. I think that the best way to approach this situation is to have multiple police force counter snipers trained to take out the target.
There's no doubt that the sniper in Dallas desperately needed to be stopped. However, using a bomb to stop him was dangerous and reckless in the extreme. There are other ways to stop a shooter that don't involve putting a huge number of people in mortal danger, and if the police don't know them, then they should be trained in them.