SAN FRANCISCO – Minutes after a shooting near the Oakland Airport this year, the gunman was on the loose. And police Sgt. Chris Bolton quickly fired off a flurry of text alerts to thousands of nearby residents through a social media tool for law enforcement agencies.

"Stay out of area," said one alert. "Multiple shooting victims reported. Medical on-scene. Police are evacuating a nearby, affected business."

Officers would eventually discover a grisly scene inside a tiny Christian college on that spring day. Seven people were killed, three others wounded and dozens terrified in the deadliest mass shooting in the city's history.