A gunman who killed 12 people at a Southern California bar posted at least one Instagram post after the beginning of the massacre, an official has said.
Social media platforms have scrubbed that and any other posts following Wednesday night's massacre.
But one law enforcement official said Ian David Long, a 28-year-old former Marine, posted about his mental state and whether people would believe he was sane.
Authorities are investigating whether he believed his former girlfriend would be at the Borderline Bar and Grill, said the official.
A second law enforcement official, Ventura County Sheriff's Captain Garo Kuredjian, said that - based on time stamps - the gunman apparently stopped shooting inside the bar and posted to Instagram.
Mr Kuredjian said he did not know the content of any posts.
Suffering from PTSD
Aerial footage from Wednesday night's shooting in Thousand Oaks.
Instagram and Facebook refuse to discuss individual accounts and did not respond to a request for comment.
Investigators have not commented on whether mental illness played a role in the killings.
But a mental health specialist who assessed Long after sheriff's deputies responded to a call about his agitated behaviour last spring worried he might be suffering from PTSD.
The incident happened in April, when yelling and loud banging noises coming from the home Long shared with his mother prompted a next-door neighbour to call authorities.
The mental health specialist concluded there were no grounds to have him involuntarily committed.