A thief swiped a woman’s wallet on 15th Street on Nov. 13 — but he picked the wrong victim: the sister of a cop.

The woman said she was between Third and Fourth avenues at around 12:25 pm when she stopped to tie her infant nephew’s shoe.

For some reason, she put her wallet on a ledge while she executed the delicate act. That’s when the perp moved in, swiping the wallet and running towards the Gowanus Canal.

The woman called her brother, an off-duty cop, who said he later caught up with the perp in the Lowes parking lot on Second Avenue.