Pure speculation. Custody transfer gone awry? When I used to work in family law, when there was significant tension (but not safety issues), I would often encourage parents to find a child-friendly, public place to do exchanges (to avoid temptation into getting into fights when someone goes to someone else's house--if there are safety issues, established child-exchange centers or, as a last resort, police stations work). Fast-food restaurants with play areas and libraries are good places, for example -- lots of folks around, and something to do for the parents/child if someone is running late. A mall food court wouldn't be too bad of a place.
So let's the parents agree to meet at the mall, but there's confusion about exactly where/when. For some reason, Mom *really* doesn't want to see Dad today (or wants to teach him a lesson because he's *always* running late). So, Mom drops the child off at the agreed upon (or not) location, and just leaves. The police get involved and take the child. Dad goes to where he *thinks* he's meeting Mom, and no one's there. Or he gets to the parking area but he's late (or, say, really early--he thought they were meeting two hours earlier than Mom thought).
Dad says he's looking for the girl at the mall until 11 pm -- what he's doing is calling Mom's cell phone, walking around the mall looking for Mom, etc. Finally he decides, "Eff it, she's messing around with my placement time, AGAIN, I'll have to call my attorney in the morning," and gives up. He's "actively" trying to get ahold of his daughter in that he's calling/emailing Mom, Mom's friends, etc. But remember, in this scenario, Mom is p*ssed at Dad for some reason, so she's turned off her phone and not checking messages.
It's the only thing that makes sense to me. Trust me, in family law, I have seen split-up parents who communicate *just* this poorly (and if there's a history of one parent not turning over the kids for placement time, it would NOT be unusual for the cops not to be called -- 99% of the time that I saw, if one parent called the cops, they would just tell them that it was a matter for family court and they couldn't do anything, even if they were showed a court order).