(CNN) After a Marine Corps veteran stormed into a country music dance hall in California and killed 12 people, investigators said there is no clear motive behind the attack.

Authorities say Ian Long , 28, fired a Glock .45-caliber handgun without a word as patrons line-danced at the Borderline Bar & Grill in Thousand Oaks late Wednesday night. He first shot a security guard and a woman working at the counter, but authorities say there was no indication he was targeting employees.

Hours after Long was found dead, apparently from a self-inflicted gunshot wound, police searched for clues at the home where he lived with his mother. As investigators dig for answers, loved ones and strangers mourn the victims -- including some now known as heroes.

Latest developments

Long served in the Marines for nearly five years as a military machine gunner and was deployed to Afghanistan, Defense Department records show.

•A mental health expert declined to commit gunman. Police were called to Long's home in April for reports of a disturbance and a crisis team felt he might be suffering from post-traumatic stress disorder, but they ultimately cleared him.

•Long's mother "lived in fear" of what her son might do, a neighbor says. She was concerned about Long, the neighbor said, but she was not worried about her own safety.

•Hundreds of people gathered to mourn the victims. "Tonight we are a hurting city but we are a community of love, of compassion and of unity," Thousand Oaks Mayor Andy Fox said at a vigil Thursday night. "We are also a community of hope."

•Authorities have not named all of the victims, but CNN has independently but CNN has independently identified some of them

Photos: In photos: Mass shooting at California bar Molly Esterline is hugged by David Crawford on the scene of a shooting at a bar in Thousand Oaks, California, on Thursday, November 8. Hide Caption 1 of 24 Photos: In photos: Mass shooting at California bar People stand in a parking lot along South Moorpark Road in Thousand Oaks in the aftermath of the shooting. Hide Caption 2 of 24 Photos: In photos: Mass shooting at California bar Investigators huddle at the command post near the bar. Hide Caption 3 of 24 Photos: In photos: Mass shooting at California bar Nellie Wong cries as Chyann Worrell holds her and Erika Sigman, right, stands beside them. All three were inside the Borderline Bar and Grill when shooting started. Hide Caption 4 of 24 Photos: In photos: Mass shooting at California bar Police work outside the venue where the shooting occurred. Hide Caption 5 of 24 Photos: In photos: Mass shooting at California bar Tim Dominguez, who was in the bar with his son, sits distraught under a freeway overpass near the crime scene in Thousand Oaks. Hide Caption 6 of 24 Photos: In photos: Mass shooting at California bar Holden Harrah, 21, right, hugs family and friends after witnessing the shooting. Hide Caption 7 of 24 Photos: In photos: Mass shooting at California bar A forensics team collects evidence at the scene. Hide Caption 8 of 24 Photos: In photos: Mass shooting at California bar An American Red Cross Disaster Relief vehicle is seen outside the Thousands Oaks Teen Center where people have come for family assistance following the bar shooting. Hide Caption 9 of 24 Photos: In photos: Mass shooting at California bar Law enforcement officers guard the road leading to the Borderline Bar and Grill. Hide Caption 10 of 24 Photos: In photos: Mass shooting at California bar People comfort each other near the scene of a mass shooting at the Borderline Bar & Grill in Thousand Oaks, Californina, early Thursday, November 8. Hide Caption 11 of 24 Photos: In photos: Mass shooting at California bar Ventura County Sheriff Geoff Dean briefs reporters on the deadly shooting. Hide Caption 12 of 24 Photos: In photos: Mass shooting at California bar A woman who fled from the shooting gets hugs from relatives in Thousand Oaks. Hide Caption 13 of 24 Photos: In photos: Mass shooting at California bar An FBI agent talks to a potential witness. Hide Caption 14 of 24 Photos: In photos: Mass shooting at California bar Officers stand near a police SUV at the shooting scene in an image from aerial video. Hide Caption 15 of 24 Photos: In photos: Mass shooting at California bar Matt Wennerstorm, still wearing a blood-stained shirt, talks to members of the media outside the Borderline Bar & Grill. Hide Caption 16 of 24 Photos: In photos: Mass shooting at California bar Investigators in hazmat outfits work out of the command center at the shooting scene. Hide Caption 17 of 24 Photos: In photos: Mass shooting at California bar People comfort each other near the shooting scene. Hide Caption 18 of 24 Photos: In photos: Mass shooting at California bar Women who fled from the shooting stand by a sheriff's deputy. Hide Caption 19 of 24 Photos: In photos: Mass shooting at California bar People await news about their friends in the Borderline Bar & Grill shooting. Hide Caption 20 of 24 Photos: In photos: Mass shooting at California bar People walk away from the shooting scene. Hide Caption 21 of 24 Photos: In photos: Mass shooting at California bar Police vehicles block an intersection near the shooting in an image from aerial video. Hide Caption 22 of 24 Photos: In photos: Mass shooting at California bar Sheriff's deputies speak to a possible witness. Hide Caption 23 of 24 Photos: In photos: Mass shooting at California bar People console one another near the shooting scene. Hide Caption 24 of 24

The shooter

Long's friends say he was a frequent visitor at the bar for years and that he liked going there.

"I would make fun of him, because he would drag me there. Sometimes we'd go there to have a drink, sit and talk, listen to music," said a woman who's been friends with Long for five years and does not want her name made public.

Authorities have identified a Facebook post believed to have been made by the shooter around the time of the attack, according to a law enforcement official familiar with the ongoing investigation.

In it, the writer says: "I hope people call me insane... (laughing emojis).. wouldn't that just be a big ball of irony? Yeah.. I'm insane, but the only thing you people do after these shootings is 'hopes and prayers'.. or 'keep you in my thoughts'... every time... and wonder why these keep happening..."

When CNN read the post to a friend of Long's, who did not want to be publicly identified, the friend said, "That does not sound like Ian to me at all. I don't know what was going through his head when he wrote this. It must have been terrible."

Long's activities in the days before the shooting remain unknown. He was a corporal in the Marines from August 2008 to March 2013, according to Defense Department records. He went to Afghanistan from November 2010 to June 2011.

Curtis Kellogg, a friend who served with Long, said the last time he spoke with Long he was headed to Southern California.

"He was excited to get out so he could go back home, ride his motorcycle again and finish school," Kellogg said.

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Long, whose Marines unit was based in Hawaii, was married in 2009 in Honolulu. The couple separated in 2011 and dissolved the marriage in April 2013 in Ventura County, California. He and his then-wife said they had no children and owned no property.

After leaving the Marines in 2013, Long went to college in California but did not complete his degree.

He was a student at California State University, Northridge, majoring in athletic training from 2013 to 2016, but he did not graduate, university representative Carmen Ramos Chandler said.

The victims

Ventura County Sheriff's Sgt. Ron Helus, 54, was among the first officers to arrive at Borderline. He was shot several times as he tried to stop the gunman.

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Helus, who loved fishing with his son, was hoping to retire in the next year or two after 29 years on the force.

Cody Gifford-Coffman, 22, lost his life shielding others, his friend Sarah DeSon said.

When the gunfire broke out, Coffman, DeSon and another friend dropped to the ground. After an apparent smoke bomb went off, Coffman stood up and told his two friends to flee.

"When he said leave and when he got up, I left," DeSon said. "I saw one opening, and I ran for it. And unfortunately, he wasn't behind me. ... He made sure people were safe, and now we all have a beautiful guardian angel watching over us."

Several victims had connections to the military.

Coffman was in the process of talking with Army recruiters.

Telemachus Orfanos, 27, was a Navy veteran who survived the Las Vegas massacre last year . After he was killed in this week's California massacre, his mother demanded actions, not words.

"I don't want prayers. I don't want thoughts. I want gun control," Susan Orfanos said. "I hope to God nobody else sends me any more prayers. I want gun control."

Dan Manrique, 33, was a Marine Corps veteran.

Justin Meek, 23, recently graduated from California Lutheran University and was planning to join the US Coast Guard. He was looking forward to cooking for everyone at the school's Veterans Day Celebration on Monday, Cal Lutheran's veterans coordinator Jenn Zimmerman said.

He had returned to the school to support the Country Line Dance Club with Borderline.

"He loved running college night and always seemed to draw a crowd," Zimmerman said.

Pepperdine student Alaina Housley, 18, was "an incredible young woman with so much life ahead of her," her aunt and uncle said.

Noel Sparks, 21, was a gifted dancer and artist, a friend says.

Sean Adler, 48, was a bouncer at the dance hall and a former wrestling coach, his team confirmed.

Four other young victims -- Blake Dingman, 21; Jacob Dunham, 21; Mark Meza, 20; and Kristina Morisette, 20 -- were also killed, the Ventura County Medical Examiner said.