He said the gunman had apparently shot himself.
Long was a veteran and served in the U.S. Marine Corps. It's unclear whether he took his own life or if the attack was terror-related.
They found Long "somewhat irate, acting a little irrationally", Dean said.
Mental health professionals sent to evaluate him concluded he did not need to be taken into custody, he said.
"I am very emotional right now", he said as he stood among other families waiting to get word of their loved ones' fates.
Thousand Oaks is a city of about 130,000 people about 64 kilometers west of Los Angeles, just across the county line.
Survivors described moments of panic and heroism.
Additional units, including SWAT personnel arrived on the scene minutes later and found 11 victims and the deceased gunman.
A GUNMAN opened fire at a bar in California killing 12 people including a cop and injuring at least ten more today. "It's something that I wish I was OK to do, but unfortunately I can't, so that's why I'm making sure that he gets remembered", King said.
"He didn't say anything, at least not that we could hear", Estron added.
Erika Sigman, 19, was another witness.
"His name was Cody Coffman, my firstborn son", said Coffman, his voice breaking as he wiped tears away with a tissue. "There is a lot of bad in this world, but there is also a lot of good and people will help", she said.
The one-hour procession through the streets was filled with sadness and silent salutes on numerous overpasses.
Nicholas Champion was among those who survived both shootings and spoke about his experience to CBS News.
There were roughly 200 people in the bar for a popular weekly "College Country" night, police said.
"He went in there to try to save people", Sheriff Dean said in a news conference. "To save other people".
The dead officer was identified as Sergeant Ron Helus, a 29-year veteran of the department, Dean told reporters. Dean said Helus undoubtedly saved lives by going in to confront the gunman.
A bomb squad was combing through the scene early Thursday morning after some witnesses reported that smoke bombs went off during the gunfire. It's also close to several other universities including California State University Channel Islands in Camarillo, Pepperdine University in Malibu and Moorpark College in Moorpark. The bar is near the campus.
California Luthern University graduate Jason Meek also died in the tragedy, the school confirmed in a statement.