Nov 8, 2018:

Late yesterday evening, a lone gunman shot and killed 12 people at the Borderline Bar and Grill in Thousand Oaks, California. At least 18 other people were treated at local hospitals for wounds or minor injuries.

One of the victims was Ventura County Sheriff's Sgt. Ron Helus who was one of the first two officers to arrive on the scene. Helus was a 29-year law enforcement veteran and was due to retire within the next year.

Police identified the shooter, a US Marine Corps veteran, as 28 year-old Ian David Long. Long was found dead shortly after police arrived, possibly from self-inflicted wounds.

Long used a .45-caliber Glock handgun to carry out the attack. The gun was purchased legally but was equipped with an illegal extended magazine.

In April police were called to Long's residence regarding a disturbance, but after an interview with a mental health specialist he was not detained.

Source:

Aarthun, Sarah; Andone, Dakin. (November 8, 2018). "What we know about the shooting at Borderline Bar & Grill". CNN. Retrieved 2018-11-08.

Thousand Oaks shooting leaves 13 people dead, including gunman, and 18 injured | Los Angeles Times

Thousand Oaks gunman was a Marine veteran who often visited the site of the shooting | CNN