Authorities haven't identified what motivated Long to open fire during college night at Borderline Bar & Grill in Thousand Oaks, a city of about 130,000 people about 40 miles (64 kilometers) from downtown Los Angeles.
The Los Angeles Rams and coach Sean McVay offered their condolences and support to the victims, families and community affected by the mass shooting Wednesday night at the Borderline Bar and Grill in Thousand Oaks that killed 12 people.
Investigators are working with the help of the Federal Bureau of Investigation to determine the identity of the shooter and a motive for the shooting.
"We will be sure to paint a picture of the state of mind of the subject and do our best to identify a motivation", Delacourt said, adding that the FBI would investigate any possible "radicalization" or links to militant groups.
Sgt. Ron Helus, a 29-year veteran of the Ventura County Sheriff's Office, was speaking his wife on the phone "as he does several times during the shift, and said to her, 'Hey, I got to go handle a call, I love you, '" Ventura County Sheriff Geoff Dean said during a press conference Thursday morning.
The Marine Corps said Long earned several awards, including a Combat Action Ribbon and a Marine Corps Good Conduct Medal.
He added, "Obviously he had something going on in his head that would cause him to do something like this". However, mental health specialists who were called in "talked to him, and cleared him".
Jerry Nadler, the top Democrat on the House Judiciary Committee, said lawmakers would get to work on legislation including universal background checks when the House of Representatives convenes in January with a Democratic majority.
Berge, who took care of Long's mother's dogs, said she told him following that incident she anxious her son might take his own life but did not fear he would hurt her.
Dean said he believed about 150 to 200 people were inside the bar at the time of the shooting.
Dean said Long was a veteran of the U.S. marine corps. "There is blood everywhere and the suspect is part of that".
At least one person was being treated for a gunshot wound, while more than a dozen others suffered minor injuries after jumping out of windows and diving under tables during the attack.
The massacre was the latest shooting rampage in the United States amid a fierce debate over gun control. Around 11:20 p.m., authorities said a lone gunman began opening fire at the scene.
Long shot an unarmed security guard outside the bar before going inside, where he fired on security staff, CNN reported.
Among those killed was a three-decade veteran of the sheriff's department, 54-year-old Sergeant Ron Helus, who was married, had a grown son and was close to retirement.
Trump ordered US flags to be flown at half-staff at public buildings and grounds.
Tait, who says she's a regular at the bar, then saw people huddled by a mirror and window and fled there.
People started trampling each other to escape, she said.
Witnesses said that people dropped to the floor and hid behind bar stools in stunned silence.
Justin Meek, 23, had recently graduated from Thousand Oaks' California Lutheran University, school officials confirmed in a statement on Thursday.