An Elk River man used a hidden camera in the dressing rooms of a Mall of America store to record women and girls while they were changing clothes, according to charges filed this week in Hennepin County District Court.

Trevor Nielsen, 42, also hid cameras at swimming pools, parks and Elk River High School, felony charges filed after a yearlong investigation say. He was charged by summons with interference with privacy involving a minor.

Last September, an employee at the mall’s Forever 21 store noticed that a man had been in a dressing room for an unusually long period. The employee thought she had seen him at the store before and had discovered a video camera hidden in a dressing room.

Police were called. When Nielsen emerged from the dressing room, they searched him and found his cellphone, a roll of double-sided tape and strips of cut tape, the charges say. Nielsen admitted that he had hidden the camera in the fitting room and said he had done the same thing before, there and elsewhere.

Before police arrived, he had been sitting in a fitting room watching the video feed he’d set up in the room next door on his cellphone, the charges say.

Police confiscated Nielsen’s electronic devices and found images of nude and partly clad women. Many were probably under 18, the complaint said.

Police found other videos from a camera that had been attached to Nielsen’s shoe or lower pant leg used to record video of women trying on clothing. Officers also found videos of students at Elk River High School and of teenage girls at pools and parks in his possession, according to the complaint.