Listed online and asked to meet with the guy. I came along as “back-up”.

She told the police she was doing that and they didn’t hesitate to come as we were already in the parking lot. When they got there the guy got nervous. SIL gave her evidence and the police told the guy something to the effect of “look, we can’t prove that you stole this stroller. But what we can do is start an investigation”

In the end this guy gave up and we walked away with the stroller.