MINNEAPOLIS — Police are investigating an Elk River man they say installed hidden cameras inside two department store dressing rooms at the Mall of America so he could record people undressing.

A search warrant affidavit filed in Hennepin County District Court this week states that four hidden GoPro cameras disguised as “electrical type boxes” were found in dressing rooms inside Hollister and Forever 21 locations at the Bloomington-based mega mall between March and July this year.

At least two of the cameras were tucked under fake shelves installed at waist-height in the fitting rooms so that they wouldn’t be easily detected.

Police arrested Trevor Alan Nielson, 41, late last month after a store manager at Forever 21 saw him enter a dressing room in the store Sept. 28, the affidavit said.

In an interview later conducted at the Bloomington Police department, Nielson reportedly admitted to installing the hidden camera “for a thrill,” and said he did the same thing about 10 other times in dressing rooms at the Mall of America and other area malls.

A Hollister at the Maplewood Mall is conducting a similar investigation after finding a hidden camera there.