Watch CNN's special series, "Deadly Fix," this week on CNN Newsroom at 9 a.m. and 2 p.m. ET.
(CNN) -- The modest clinic on Milpas Street in laid-back Santa Barbara, California, was well known to patients seeking powerful pain medication.
They went there to find the "Candy Man."
Dr. Julio Diaz earned that nickname because, according to court records, he was writing prescriptions for massive numbers of pills -- hundreds, even thousands, at a time. He prescribed medications like oxycodone, a powerful opioid pain killer that is highly addictive.
At the nearby Cottage Hospital, emergency room doctors noticed a pattern and sensed a problem.
"We communicate first with our patients and then with the primary care providers. We then began to see that there was a pattern and that clearly by far Dr. Diaz's prescribing stood out above any of the other physicians in the computer," Dr. Chris Lambert said.
Lambert found that Cottage Health documented more than 400 emergency room visits from Diaz's patients, according to court documents. Some were clearly dependent on opiates, he said, and others were seeking more pain medication.
"And of course we saw the complications, too," Lambert noted. Those complications included symptoms of severe drug withdrawal and overdoses.
The Medical Board of California, and eventually the Drug Enforcement Administration, were called to investigate. That investigation resulted in a laundry list of charges against Diaz including the over-prescription of narcotics, prescribing narcotics when there was no medical need, and illegal distribution of a narcotic to a person under the age of 21.
According to the DEA, there were a dozen overdose deaths associated with Diaz. Twenty-seven-year-old Adam Montgomery was one of them.
Montgomery started seeing Diaz after he injured his back on a construction job. He was seeking pain medication. He got it, and soon he was hooked.
As the months went by, Montgomery's parents noticed a change.
"Well, at some point, he started spending a lot of time in bed. And just watching TV, never doing anything," Adam's father, Robert Montgomery said. "And that seemed to get worse and worse. And then I noticed the color change in his face, his attitude, his love toward his family ...That all went away."
Montgomery slowly became aware that his son was addicted to oxycodone, and he called Diaz.
"I was seeing paperwork with hundreds of oxycodone pills," Montgomery told CNN. "I wanted to know why he was giving him so many." He says he never got an answer.
In an affidavit, the DEA alleges that in the six weeks before Adam Montgomery's death, Diaz prescribed him a total of 2,087 pills, an average of 63 pills a day.
On the day after Thanksgiving in 2011, Montgomery received the news that his son had died of a drug overdose. In Adam Montgomery's bedroom and car, investigators found bottles of multiple drugs, and some were empty. All were prescribed by Diaz.
The autopsy concluded that a cocktail of oxycodone, hydromorphone, alprazolam and methadone was the cause of death.
"Right now we have more people that are dying from prescription opioids than cocaine and heroin combined," said Robert Hill, a DEA special agent with years of experience on the front lines of the war on drugs.
Hill says that in 2011, the most recent year for which there are statistics, more than 22,000 people died from prescription drugs.
Late last year, Diaz signed a plea agreement, admitting to a reduced number of charges. Those charges include the illegal distribution of oxycodone, hydromorphone, alprazolam and fentanyl. The original charges against him carried a maximum sentence of 200 years in prison and up to $10 million in fines, but the plea bargain will likely reduce that sentence.
CNN contacted Diaz's attorney, but received no comment. Diaz awaits sentencing.
To this day, Montgomery's parents struggle with the what-ifs.
Had he known then what he knows now, "I might have been able to save him, but I was more disappointed in him -- in making these bad decisions," Robert Montgomery said. "But it wasn't him, it was the drugs that changed him. So I just turned my back on him, and I wouldn't do that today."
Watch CNN Newsroom weekdays 9am to 3pm ET and weekends. For the latest from the CNN Newsroom click here.