This all feels sadly familiar.

As Twitchy told you, a gunman opened fire at the Borderline Bar & Grill in Thousand Oaks, California. At least 12 people — including heroic Sheriff’s Sgt. Ron Helus — are dead. And it appears that once again, red flags went ignored until it was too late.

Law enforcement authorities were apparently well acquainted with the suspect (we’ve blacked out his name and photo):

Ugh. More from Fox News (we’ve left out the suspect’s name):

Sheriff Geoff Dean, who is set to retire on Friday, said [the suspect] may have suffered from post-traumatic stress disorder and was known to law enforcement officials due to several unspecified “contacts” stretching back multiple years. [The suspect] served in the Marine Corps from August 2008 to March 2013, with a deployment in Afghanistan between November 2010 and June 2011, military records show.

“We’ve had several contacts with [the suspect] over the years, minor events such as a traffic collision. He was a victim of a battery in a bar in 2015,” Dean said, adding that the bar in 2015 was a different establishment than Borderline.

Dean said the last interaction between [the suspect] and authorities occurred in April, when police officers were called to Long’s house in Newbury Park, about five miles from Borderline, after reports of a disturbance. When they arrived, officers found Long “irate and acting irrationally,” leading to a crisis intervention team being summoned. The team, however, cleared [the suspect] and said they didn’t feel he was qualified to be taken into custody.

“Obviously, he had something going on in his head that would cause him to do something like this. Obviously, he had some sort of issue,” Dean said of [the suspect].

Obviously. The question is whether law enforcement did their due diligence with regard to the suspect. Based on the sheriff’s remarks, it’s not clear that they did.

The suspect is dead. At least 12 people are dead. Nothing can be done to stop the suspect now, but hopefully going forward, authorities can pay closer attention to mental health issues — and they’ll be in a better position to take action to prevent future tragedies like this one.