The question of eventual martial law remains to be answered — the fedgov keeps aiming at a federalized police force. We haven’t heard all the echoes of this event yet. But it is the beginning of robotic law enforcement. I don’t doubt that as a major American city, Dallas (PD) had obtained a robot or the purpose of remote detonation of suspected bombs — all too likely these days. They would’ve kept its LiPO4 battery on a maintenance charger, whether or not it was being routinely dusted. It may even have been housed in one of the SWAT vans they either rolled when the shooting began, or possibly had on site as a precaution.
I’d hope that such robots are versatile enough platforms, that they may be equipped with capture/disabling devices as well as shaped charges and firearms. In a hostage situation, the potential danger to hostage(s), may render the one-blast-kills-all solution too politically risky to be useful.