Nevada shooter Alan Oliver Frazier sparked havoc in a Reno medical building, as caught by 911 tapes showing dozens of people calling 911 while hiding in examination rooms and bathrooms from the suicidal gunman. Frazier shot two doctors, one of whom worked at the urology clinic the Nevada gunman claimed performed the vasectomy that "ruined his life."

Soon after charging into the Urology Nevada office the previous week, 51-year-old Frazier warned patients and visitors of the hospital to leave the premises, threatening to shoot them if they didn't cooperate. The Nevada started to open fire using a pistol-grip, 12-gauge shotgun soon after the threat.

The shooter, who hailed from Northern California, expressed his anger over the reportedly botched vasectomy he'd had in the medical center three years ago which "ruined his life," reported one male witness who heard from the locked bathroom he and ten other people hid during the incident.

"He says, 'As long as you're a patient, you can leave. Otherwise I'm going to shoot you,'" the witness explained. The bathroom where he'd been hiding was just opposite the urology office where the Nevada shooter started opening fire.

One woman hid under a desk and called 911, talking so lowly that her voice could barely be heard.

"I hear gunshots outside my office," the woman said over the phone to the 911 dispatcher. "I just heard another one. ... He's going to (expletive) kill us." The woman continued talking softly into the phone, mentioning when Frazier passed by her.

One of the 50 calls the police claimed they got on December 17, just after 2 p.m. when Frazier was still in the building, was from a woman hiding in a locked officer, hyperventilating and gasping for breath while she talked.

She reported that Frazier was in the middle of the office and had shot one of the hospital's doctors.

Police had responded and arrived at the Reno medical center within minutes after the calls and rushed into Urology Nevada as calls asking for help continued to stream in.

The Nevada shooter, a former worker in a power plant, wrote in a suicide note he left behind that he planned this attack and that his targets were the doctors of Urology Nevada, confirmed police investigators. No information has been disclosed on who operated on the gunman, who resided near Lake Almanor.