Peter Hermann

The ruling, released Monday, probably will make it difficult for prosecutors to pursue homicide charges in Brian Sicknick’s death.

The driver of a tour bus that fatally struck Monica Carlson and her mother last week was charged with two counts of involuntary manslaughter.

Cellphone video has become as much a part of policing as tickets and handcuffs. Video images of police shootings have sparked national turmoil. But Friday’s ugly, cacophonous scene in McKinney, Texas, at first seemed like something more routine — a call about misbehaving teens at a pool party on a hot Texas afternoon.