Or the perpetrator paid the driver of the van to deliver a message..... or maybe just to show up and confound the police. It wouldn't be difficult to find someone willing to do it: you just have to know where to look.
Earlier in the thread, a witness was quoted as saying that the police were waiting for the minivan. The chief's crypytic message makes perfect sense now: the perp probably gave them the number of the pay-phone and told them to expect a call/message there.