Boston transit police on Friday charged a man with the indecent assault of a 4-year-old at a Massachusetts Bay Transit Authority station near the Boston Common.

Officers said they were called to the Park Street Station by the child’s mother, who told them her child was assaulted by a man she didn’t know on the westbound Green Line platform.

She told investigators she confronted him and took a photograph of him with her cellphone, transit police said.

Armed with the photo and the help of a witness, officers tracked the man down several miles away and took him into custody.

He was identified as George Francois, 66, and he was charged with indecent assault and battery on a child under 14.

Francois reportedly made incriminating statements to the arresting officers, transit police said.

No further details were provided.

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[Featured image: Park Street Station/Google Maps]