May 21, 2010 -- Aaron Vargas, a young father who fatally shot his former neighbor and claimed he had been sexually abused by him, said he regrets killing Darrell McNeill.
"I'm still trying to make sense of the situation," Vargas told "20/20's" Chris Cuomo in an exclusive interview. "It's not up to me to decide someone's fate."
On a February 2009 night in Fort Bragg, California, Vargas visited McNeill's trailer and killed him with a single shot to the stomach. But Vargas told Cuomo that killing the 63-year-old man was the last thing he ever wanted to happen.
"I didn't go to there to shoot the guy. I went there to warn him off," Vargas, 32, said. "He [McNeill] needed to stop. That's for sure. He didn't need to be shot and killed. But he needed to be stopped."
Within hours of the shooting, Mendocino County sheriff's investigators arrested Vargas and indicted him for first-degree murder. Vargas pleaded guilty to voluntary manslaughter in March and is expected to be sentenced next month. He is facing up to 10 years in jail.
Vargas said he doesn't belong behind bars.
"If the law doesn't work, ... it doesn't work," Vargas told Cuomo, adding that police had "plenty of chances" to arrest McNeill.
After the incident, Vargas' family said several men in their 30s and 40s came forward saying that they, too, had been abused by McNeill. One said they had warned the Fort Bragg Police but no action was taken.
"He [McNeill ] was actually damaging people and it wasn't a game anymore. You know? He played his whole life like it was a game," Vargas said. "He'd see that, finally, this wasn't going to keep going. And we weren't going to be little puppets anymore."
Vargas Says Abuse Made Him Feel 'Shameful'
Vargas grew up next door to the McNeills and was close friends with McNeill's son, Michael. "Up until around middle school, I was a happy kid," Vargas said.
But at age 11, Vargas said, McNeill first took advantage of him on a fishing trip. In his teens, McNeill continued to single out Vargas, using drugs and alcohol, Vargas said, to lure him to his home.
"It happened many times when I wasn't even conscious ... just be totally gone," Vargas told Cuomo, adding that he knew it was wrong and felt "shameful" afterwards.
To escape the embarrassment, Vargas said, he turned to alcohol and would binge drink. He was arrested on several DUI charges and couldn't hold down a job. His family saw him struggling, too, but never understood why.
"Everything would seem fine. He'd have a job ... he had a girlfriend, he seemed happy, had it together," said Vargas' sister, Mindy Galliani. "Then, all of a sudden, it's like his whole life would fall apart. ... My family and I would discuss it at times. You know, we would wonder, 'What's going on with Aaron?'"
Now, Galliani said, it's clear what was behind her brother's meltdowns. "It was Darrell ... coming into his life," she said. "Aaron moved out of town and that's when he would do fine for a while. It was a pattern of Aaron getting away from Darrell and Darrell finding him and that's what would cause Aaron's world to just fall apart."
Baby Girl Makes Vargas Want to Be a Better Man
But Vargas' world changed for the better in 2008, when he proposed to his girlfriend of eight years, Selena Barnett. While they were planning their wedding, they learned Barnett was pregnant and soon welcomed a little girl, Josie, into their lives.
Vargas said the birth of his daughter was life-changing. "It made me want to be responsible," he said. "I want to make myself the best guy I could be."
But Vargas said no matter how hard he tried to keep his distance from McNeill, the cycle of abuse would begin again, and he would somehow lure the young father back.
Forensic psychiatrist Dr. Michael Welner explained how McNeill could have a tight hold on a grown man such as Vargas.
"You take someone who is vulnerable, and you get them formative, and you attach them all through their development, and you get in their DNA," Welner said. "And that's how you have people, who even in adulthood, are doing things totally unacceptable to them. And yet at the same time, they're powerless to break away from it."
Power of Love Pushed Vargas to Act
In the months leading up to the shooting, Vargas said, McNeill tried to tighten his grip. "He'd call almost daily," said Vargas, who was unsuccessful at trying to push McNeill away.
Then, one day, McNeill asked to babysit for his daughter. "I can't describe that feeling," Vargas said. "If he [McNeill] came around when I wasn't there, that he'd, you know, touch my daughter in some funny way when she wasn't being guarded."
The thought of what could happen to Josie, Vargas said, enabled him to stand up to McNeill. He finally went fishing to clear his head but a few drinks turned into many and that's when he went to McNeill's home with a gun.
"I remember showing him the gun. And ... tell him, 'Listen, I'm not joking. And you're going to stop doing what you're doing and you're not going to hurt anybody anymore,'" Vargas recalled.
But pulling that trigger set off a series of events that would expose McNeill's secret world and rally an entire town around a killer. Vargas told "20/20" he doesn't see himself as a hero or a vigilante.
"Just somebody that wanted the guy to stop ... that couldn't be stopped," Vargas said. "Sometimes, I guess people can ... take control over you in ways that you would never imagine."
Childhelp.org, one of the leading organizations working on the treatment and prevention of child abuse, has identified warning signs that your child may have been sexually abused. Click here for more information.