My 7mth old son's dad doesn't want to return him back to my care. what can i do to get him back in my care?

my baby's father and I have been separated for 3 months and i currently have filed child support on him and it's still being processed .on 10-20-09 he had him for the night and didn't want to return to me the next morninig 10-21-09 i called the police they came and said I couldn't leave with him and couldn't do anything about it because they needed to see doents saying that i was the custodial parent. what can i do to get him back lawfully....? if i go to visit him at his father's home and i am holding him in my arms can i call the police and walk out with him by law...?