Former ATF agent says he regrets his last assignment. It changed how agencies approach undercover work.

• Billy Queen's undercover ATF mission infiltrating the Mongols was supposed to last a few months.
• It stretched on for two years, costing him his personal life and role as a father, he says.
• The operation's aftermath forced agencies to rethink undercover strategies and prioritize agent safety.

After nearly two decades working undercover for the Bureau of Alcohol, Tobacco, and Firearms, Billy Queen was given the most dangerous assignment of his career: to infiltrate one of the most violent biker gangs in Southern California, the Mongols.

Within the first few months, his mission had already escalated beyond its original scope. What was expected to last a few months stretched into a multiyear infiltration that reshaped how agencies handle deep-cover operations.

Over time, Queen became a trusted member of the gang and eventually its secretary-treasurer, giving him exclusive behind-the-scenes access to the gang's criminal activities across the nation.

In 2000, the operation concluded, resulting in 54 arrests and 53 convictions. The ATF called the assignment one of its most successful biker gang infiltrations to date, but Queen says the outcome came at a personal cost he didn't fully understand at the time.

"Had I known what it was going to cost me, I'd have never done that," he said.

The job took over his life

Infiltrating a group as violent and dangerous as the Mongols wasn't the type of undercover operation you can step in and out of, Queen says. "There was no such thing as time out. It was 24/7."

Over time, he lost contact with his children, his girlfriend, his friends, and his colleagues. By about a year and a half into the operation, he says he had no one outside the gang members he hung out with and only limited contact with his ATF handler.

"I'd lost everything. I didn't have a personal life anymore," he said.

The line between his real identity and his undercover persona — Billy St. John — began to blur. Queen described a pivotal moment when gang members supported him after his mother's death.

He flew across the country to bury her. He recalls that the ATF was only interested in his returning to the gang, saying nothing about his loss. But upon his return, numerous gang members hugged him, told him they loved him, and said they were sorry for his loss. This emotionally complicated Queen's role as an informant.

"I wanted to be Billy St. John. I didn't want to be Billy Queen," he said. "I wanted to ride off with those Mongols."

At the same time, he witnessed extreme violence — including gun running, brutal beatings, rape, and murder — that reinforced why he was there in the first place.

"One day I loved them. Next day, I hated them," he said.

The aftermath exposed the real cost

Two years into the operation, Queen felt he was at serious risk of being exposed. So, he left the gang and immediately entered a witness protection program run by the ATF.

He was relocated to Texas while his family was relocated to Florida. He was given a new identity and told that ATF would fly his children to him to visit while he stayed in Texas waiting to testify.

"For the next two years, I got to see my children one time. I was never going to be a father again," he said.

At the same time, he says Mongols members were actively looking for him and threatening to kill him.

"I was absolutely alone," for those two years, he added.

The case forced agencies to rethink undercover work

Queen says the operation succeeded in dismantling a violent organization, but it also exposed gaps in how agencies managed long-term undercover assignments.

In particular, he says the model of sending a single agent deep undercover without sustained support proved too risky.

After his case, agencies began using teams rather than relying on a single operative and became more cautious about assigning agents with families to extended undercover roles, Queen says.

Queen's experience showed that the danger doesn't end with the operation — and that the personal fallout can extend for years.

Even now, Queen says the risk to his life remains. "There are still guys with the Mongols that could kill me," he said.

He no longer lives in hiding. Instead, he relies on constant awareness and personal protection.

"When I went home, I made sure that all my guns were locked and loaded," he said. "If they're going to come and get me, I'll be ready."

Business Insider was unable to reach ATF for comment.