The Marine Corps veteran who slaughtered 12 people at a California club posted on social media that he was bored during the horrific attack, law enforcement officials said Friday.

Ian David Long, 28, posted on an unspecified social media platform that he wasn’t crazy — just bored, NBC News reported.

He also wrote that he knew his mental state would be a topic of debate for years to come, and wondered whether people would believe he was sane, officials said.

Investigators looking into a motive for Wednesday night’s mass shooting at Borderline Bar & Grill in Thousand Oaks are also looking into whether Long, a former US Marines, believed his ex-girlfriend would be at the club.

With Post wires