Okay, you've piqued my curiosity. Why?
Just as guess............Well, since Livingsone and Kennedy came to the building in two cars and had to (or chose to) leave in just one car, there is a possibility that, in their haste to shove a set of keys into Vince's pocket (like the Keystone Cops) one of them shoved one of their own sets of keys in Vince's pocket by mistake. Nah! But why did they leave in only one car?
Whadaya think?