THOUSAND OAKS, Calif. (AP) — The gunman who killed 12 people at a country music bar in Southern California went on social media during the attack and posted about his mental state and whether people would believe he was sane, a law enforcement official said Friday.

Also, one of the possibilities investigators are looking into is whether gunman Ian David Long believed his former girlfriend would be at the bar, the official said.

Authorities have not determined a motive for Wednesday's night rampage at the Borderline Bar & Grill.

The official — who was briefed on the investigation but not author...