huh?

There was a post recently that questioned how Red knew Liz had shot Tom Connolly before Liz had the chance to tell him. I think there may have been enough time for Cooper to call Red before the authorities arrived at the scene. It's just my best guess. But I think there is another mystery here...Liz is walking down the street right after shooting Connolly. She walks past someone on the street and steals that person's cell phone. Liz first calls Ressler and then she calls Red. Red answered the phone, "Lizzie". Would someone please explain to me how Red knew it was Lizzie on the phone if she was calling from a stranger's cell phone?????