(CNN)Back in April, officers in Thousand Oaks, California, responded to a disturbance at the home where Ian David Long lived.
CNNs Jose Pagliery, Shimon Prokupecz, Scott Glover, Paul P. Murphy, Cheri Mossburg, Ryan Browne, Sonya Hamasaki and Joe Sutton contributed to this report.
Video: At least 11 injured in shooting at California bar
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Ventura County Sheriffs Office remembers fallen colleague Sgt. Ron Helus, who was killed after responding to calls of gunshots at Californias Borderline Bar & Grill.
The California sheriff's sergeant first on the scene at Wednesday night's mass shooting heard gunfire booming inside the bar and instinctively ran into the crowded venue — where he "died a hero," one of 12 people killed by a former Marine who ended the massacre by committing suicide.
Sheriff's Sgt. Ron Helus – who was nearing retirement in about a year — "gave it his all" but was shot multiple times by 28-year-old gunman Ian David Long and later succumbed to his injuries at a hospital, Ventura County Sheriff Geoff Dean said.
The first reports of shots fired at the Borderline Bar & Grill in Thousand Oaks came in around 11:20 p.m. on a night the packed bar was hosting a special "College Country Night" event. Dean said Helus made one last call before heading to the scene: to his wife.
Video: Deadly Shooting At Bar In Southern California
At Least 12 Killed In Mass Shooting At Southern California Bar
Sgt. Ron Helus was among the 12 people killed when a gunman opened fire inside Borderline Bar and Grill. (Ventura County Sheriffs Office)
Helus was having a conversation with his wife on the phone at the time he got the call about the shooting, as he does several times during his the shift, according to Dean.
"He said to her, 'I gotta go handle a call, I love you. I'll talk to you later,'" he told reporters.
The sheriff said it was only three minutes later that Helus made entry to the bar with two California highway patrol officers. The cops believed there were other victims still trapped in the bar, but as Helus entered the front door, he was struck "multiple times" by gunfire.
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“They knew they had to take action, and they went in and did what they had to do," Dean said.
"You know we go to the gym together, work out together, and its horrific and terrible and it saddens our heart," said Dean, who appeared visibly emotional and on the verge of tears.
"There's just no way to describe this," he said. "It saddens us all and it tears at our hearts and emotions as it should."
His colleague, Sgt. Julie Novak, told "FOX & friends" that Helus was "an amazing guy" who loved helping people.
Ventura County Sheriff Geoff Dean told the media that 911 had received multiple calls that a shooting was taken place at the Borderline Bar and Grill at around 11:20 p.m. Pacific time on Wednesday night. He identified the sheriffs sergeant who died as Ron Helus. He said that the suspect, who has not been identified but is thought to have acted alone, was dead when more officers arrived on the scene. Helus died at a local hospital; the bodies of the other 11 were found at the bar when other officers arrived.
Video: Press conference: Mass shooting at California bar
"He probably should have retired a couple years ago, he could have, but he stayed on because he loved the fight," Novak said. "He loved helping people, he loved protecting people. He did exactly that tonight."
Video: Press conference: Mass shooting at California bar
Ventura County Sheriffs Sgt. Ron Helus was a 29-year veteran of the department, and was planning on pursuing his doctorate degree, according to his LinkedIn. (Facebook)
Novaks said that Helus went into the building with "no idea" what to expect — only knowing he wanted to help those inside.
One witness to the shooting, Matt Wennerstrom, told reporters that the shooter had a handgun and that he had first noticed him opening fire on employees at the bars front desk. He said he and other patrons had smashed some of the bars windows and helped other people escape through them.
Thousand Oaks shooting: These are the victims and their stories
The California Highway Patrol officers that accompanied Helus into the bar ended up rescuing him when Long opened fire.
Ventura County Sheriffs office Capt. Garo Kuredjian says the first reports of gun shots happened at 11:20pm Wednesday night at the Borderline Bar & Grill in Thousand Oaks, California, about 40 miles west of Los Angeles.
Ventura County Sheriffs Sgt. Ron Helus was looking to retire in the next year or so, according to Ventura County Sheriff Geoff Dean. (Facebook.)
California shooting survivor also survived Las Vegas shooting
Helus' LinkedIn page showed he was an FBI certified firearms instructor and a POST — Peace Officer's Standards and Training — instructor. He earned a master's degree from the University of Oklahoma, and had planned to pursue a doctorate degree in the "near future."
"I have thousands of hours of specialized training," he wrote." I work or have worked, the following assignments: Custody; patrol (Deputy, Senior Deputy, Sergeant); SWAT; all aspects of firearms, less lethal, and chemical agents instruction; investigations; narcotics; and wellness advisor."
Tyler Spady describes the terrifying moment the gunman aimed at the crowd he was in at Californias Borderline Bar & Grill.
“Dan’s life was dedicated to serving others, during his military career and beyond,” said John Pinter, executive director of Team RWB. “We offer our deepest condolences to the Manrique family and ask that our Eagles around the world join us in keeping all those impacted by this tragedy in your thoughts and prayers.”
In a series of tweets, President Trump praised Helus and the "great bravery shown by police."
The attack on the bar – a college favorite that was hosting a country music event – was the nation's deadliest shooting since 17 students and teachers were killed at a Parkland, Florida, high school nine months ago. It also came less than two weeks after a gunman massacred 11 people at a synagogue in Pittsburgh.
"California Highway Patrol was on scene within 3 minutes, with first officer to enter shot numerous times," the president said. "That Sheriff’s Sergeant died in the hospital. God bless all of the victims and families of the victims. Thank you to Law Enforcement."
"The thoughts of every #NYPD member this morning are with the families & colleagues of all those killed or injured in the shooting inside a Thousand Oaks, Calif., bar — 12 innocent lives taken, including the first Ventura County cop on the scene: Sgt. Ron Helus, a 29-year veteran," New York Police Commissioner James P. O'Neill said.