The FBI was carefully examining Thursday the vehicle and home of the gunman who killed 12 people at a bar in Thousand Oaks, Calif.
Each moment was captured by TV cameras and broadcast live on cable networks as Americans grappled with another mass shooting.
Paul Delacourt, assistant director of the FBI's Los Angeles office, said it appears Long acted alone.
'All I wanted to do was get as many people out as possible, ' he said while wearing a bloodstained t-shirt.
Dean said the other prior encounters were a traffic accident and an incident when he was the victim of battery at a bar.
Dean said that the dead police officer, who was named as Ron Helus and had been on the force for 29 years, was among the first on the scene. Long 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.
The sheriff said a mental health crisis team was called at that time and concluded that Long did not need to be taken into custody.
Police say Long was dressed in black from head to toe.
Witnesses told CNN that he used a short-barrelled shotgun, while others told local media that he carried a "smaller-calibre handgun with a light or laser attached to the bottom of it".
Knapp said he helped people hide behind a pool table and then fled outside, alerting people on an outdoor smoking patio and helping carry a victim to an ambulance. Some threw barstools through windows to escape.
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Later, he enrolled at nearby California State University, Northridge, last attending in 2016, the school said in a statement. A GUNMAN opened fire at a bar in California killing 12 people including a cop and injuring at least ten more today.
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Friends are remembering sheriff's sergeant who was killed trying to stop a shooting rampage at a California bar as a "cop's cop" who didn't hesitate to run toward danger.
Jasmin Alexander, who was with around 15 friends at the bar, said there was chaos and confusion inside when shots rang out. "He was found inside an office just adjacent to the entry to the bar".
Borderline Bar and Grill in California had become a safe haven for dozens of survivors of last year's massacre at a Las Vegas country music festival, a place where they gathered for line dancing and drinks.
Map of California locating shooting at a bar in Thousand Oaks. "You can't go to a bar or a nightclub?" He also wrote, "God bless all of the victims and families of the victims".
More recently he was living in a home where neighbours said they could hear frequent, aggressive shouting between Long and his mother, especially over the past year. He was a machine gunner.
That, in turn, closely followed the series of pipe bombs mailed to critics of President Donald Trump.
Trump ordered USA flags to be flown at half-staff at public buildings and grounds.
The top Democrat on the House Judiciary Committee, Jerry Nadler of NY, said lawmakers would start crafting a gun-control bill when the House convenes with a Democratic majority in early January.
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Thousand Oaks is in Ventura County, about 40 miles from downtown Los Angeles. Thousand Oaks was considered the third-safest city in the US this year, according to Niche, an online company that provides data on neighborhoods, companies and schools.