Frederick McLean is one of the U.S. Marshals "Most Wanted Fugitives” and could be living in San Diego County. The suspected serial child molester has been on the run for more than a decade

For Deputy U.S. Marshal Tom Maranda, his only mission is to catch McLean.

“I really dislike this guy. I really do,” Maranda said.

He says the elusive child molester has been on the run since 2005 when one of his victims confronted him.

“He had molested her dozens of times. Over a hundred times,” he said.

But Maranda says the string of victims goes back decades

“The part that literally at times keeps me awake at night is…he's not going to stop,” Maranda said. “This guy is predator through and through. The longer I don't find him, the more victims he's adding to his list.”

McLean was a Jehovah's witness -- using the religious community to lure his targets. He'd say things like, “We're members of the same church. Why don't you let me take your kids camping?”

The Marshals say he then sexually assaulted girls between 8 and 12 years old.

10News asked Maranda what made this particular fugitive so hard to find.

“People trust him because they don't view him as threatening,” he responded.

Maranda described McLean as plain looking, soft spoken, and unassuming, so he can blend in almost anywhere.

“This guy could stand behind you at Walmart and you wouldn't look twice at him,” Maranda said.

He says that "nice guy" demeanor makes this case even tougher to crack.

McLean previously owned a business restoring and selling old race cars. His last known location was Hemet in Riverside County, but Maranda gets new tips each week -- some from all over the world, including South America, Central America, Mexico and Europe.

After years of searching, the case still haunts Maranda.

“What he does is like an assault on my psyche, on my soul,” Maranda said.

The veteran deputy can't help but think of his own daughter. He also feels a sense of responsibility for the victims.

“Because he's still out there, they still have nightmares,” Maranda said.

He's confident the Marshals will eventually find McLean, but until then, one particular family photo is all the motivation he needs.

“It's him at Alcatraz standing in a jail cell. It hangs on my wall,” he said. “That's the dream.”

The Marshals say McLean is an experienced camper and has visited the Anza-Borrego desert and Cuyamaca mountains.

If you have any information or have seen Frederick McLean, call the Marshal's tip number 1-800-336-0102 or click here.