Charges have been filed against 11 people caught trespassing in a Fridley sewer system Monday night.

The suspects, ages 18 to 35, said they were members of a group exploring the tunnels that carry wastewater and contain utility lines underneath the BNSF rail yard and a public works water facility, according to charges of trespassing critical public service utilities and underground pipelines utility infrastructure filed Tuesday in Anoka County District Court.

A resident living near the 4500 block of NE. Main Street called police about 7 p.m. after seeing four people remove a manhole cover and climb into the sewer system. The resident also reported several vehicles parked near his home.

Officers responded to the area and later saw three suspects emerging from the manhole, Fridley police reports said. Officers arrested the suspects at the scene and learned others were in the sewer system.

One suspect told police he picked up a friend and drove to Fridley to explore the storm sewer. He told police he entered the system on Main Street and walked underneath the BNSF rail yard to the Mississippi River, where he climbed out, a police report said.

The mother of another suspect told police her son is autistic and "hangs out with people that consider themselves as 'urban explorers,'" a police report said.

Police found three other suspects who "smelled strongly of sewage" walking on East River Road and arrested them, an officer's report said.

Officers transported the suspects to the Anoka County jail, where on Tuesday 10 of them were being held without bail: Jacob Flaherty of Cottage Grove; Miki Aili of St. Paul; Eric Skog and Andrew Quick of Eagan; Trevor Krawchuk of Oakdale; Josie Haigh and Justin Schneider of South St. Paul; Stacia Gillette of Roseville; Michael Johnson of Rogers; and David Perrine of Inver Grove Heights.

Justin Peterson, who is autistic, was released to his guardian and charged with a formal complaint.

All but Quick, Peterson and Flaherty will appear before a judge at 9 a.m. Wednesday. The three others will appear at a later date, court records show.