MARYVILLE, Ill. (AP) -- Greg Kellerman once drove to Canada to get his man -- on tape.

There was the time he caught another man on camera smoking crack cocaine. He taped another in Springfield who was lifting and moving 250-pound motorized children's vehicles while receiving workman's compensation benefits. He even tracked down rapper Nelly's manager in Carbondale to serve him court papers.

"It was over a fight (Nelly) allegedly was in," Kellerman said. "So a private investigation firm in St. Louis asked me to go to down Carbondale to serve Nelly, and so I made it through his group of security and was able to serve his manager."

It's all in a day's work for Kellerman, who recently moved his Kellerman Investigations from his home to a new office in Maryville. His job is to conduct surveillance for infidelity and workman's compensation fraud cases. His firm also serves papers for attorneys, individuals and businesses.

Kellerman's business has grown to the point that he is serving an average of 1,500 papers and conducting approximately 400 prescreenings and background checks a month. In that span, he also will conduct as many as five domestic surveillance tapings for clients who suspect their spouse is unfaithful.

"Most times, the client just wants to know their suspicions are correct, so I provide it through video surveillance," he said.

Kellerman is able to track and follow suspected cheaters and videotape them in an apparent sexual act with another and provide documentation to his clients.

He said he got within 12 feet of a man he found in Vincennes, Ind., and taped the man smoking crack cocaine in front of his child. But other than serving papers, all he does is tape record. He's not there to apprehend fugitives -- he only catches them in the act.

"We're just observers with a camera," he said. "We never confront. If we did, we're not doing our job properly and will not stay in business very long. If I'm doing my job correctly, you would never see me unless the client requests you be seen."

His footage aided in the arrest of the man caught smoking crack cocaine in Indiana.

"I just pointed him out to police, who arrested him," Kellerman said.

Kellerman also spent four days searching for a fugitive before finding him in Ottawa. "He wouldn't come across the border because he thought I was going to arrest him, but I was only going to serve him papers," he said. "Which is what I did."

Kellerman's business has also attracted the people who produce the reality TV show "Cheaters." Kellerman Investigations works with the producers, who film all of their infidelity encounters in Texas. In turn, Kellerman has access to Cheaters' private investigation firm's data base, CNET. It provides the metro-east investigation agency state-of-the-art communications and its clients have access to GPS tracking units.

Kellerman's expanding business comes as demand grows for private investigators. According to the U.S. Department of Labor Bureau of Labor Statistics, employment of private detectives and investigators is expected to grow faster than most occupations through 2014.