LONGMONT, Colo. -- Longmont police have arrested a 46-year-old man suspected of serial child sex assaults in three states over a period of 20 years.

Called "Uncle Bear" by the children he allegedly molested, Lonnie Hall had apparently been moving from among relatives' homes in three states, according to an affidavit released Wednesday.

"His pattern was very much with children to embed himself in a home and develop a trust with these adults and children in the home and develop the sexual relationship with the children," said Cmdr. Tim Lewis of the Longmont Police Department.

The arrest warrant accuses Hall of rubbing his genitals on the children and forcing some children to help him masturbate with his clothes on.

While dozens of names are redacted, it appears there may be six young victims, all ranging in age from 4 to 9 years old and all relatives of Hall.

Hall was arrested at his job in Denver on Tuesday after a monthlong investigation.

A multi-jurisdictional task force -- the Fugitive Location and Apprehension Group -- along with Denver and Aurora police officers, helped U.S. Marshals and Longmont officers make the arrest Tuesday afternoon.

Hall was working with a cleaning crew assigned to a Kaiser Permanente medical building at 20th Avenue and Franklin Street.

"It was yesterday around noon we found out he was working at this hospital. And we moved on it by 6:00 last night so that we could shut that down," Lewis said.

Hall also has an extensive criminal background with arrests for domestic violence and burglary dating back at least as far as 1998.

A Kaiser Permanente spokeswoman told 7NEWS this incident will prompt them to review their employment screening processes for all contractors.

Hall was arrested on suspicion of five counts of sexually abusing children, with a pattern of abuse. He was being held in the Boulder County Jail with bond set at $50,000.

The investigations in other states -- including Nevada and Louisiana -- is ongoing, Lewis said.

If anyone believes that they or their children may have had contact with Hall they are asked to call Longmont Police at 303-651-8501.