Quick question about Sirius

[Cindy C.]

No: HPFGUIDX 28050

Early in PoA, Sirius find Harry near Privet Drive, and later he 
reveals that he knows Harry lives with his aunt and uncle.  How does 
he learn this?  Does Crookshanks tell him?  Does he learn it the 
night Harry's parents died, and if so, why would he know this if 
MacGonagall didn't know until Dumbledore told her?  Does it have 
something to do with the missing 24-hours?

I swear, I searched the board for the answer to this question and 
couldn't find it.  Sorry.

Cindy