30 days notice from tenant ? Security Deposit question

Hi,
I have an apt in Brooklyn, NY and also had a roomate. He all the sudden decided to move out which lead me to believe he had been looking for a while longer than he let me know. Anyway, I asked him when he was planning to leve as he wanted me as a referrance for his applications. He said he wasn't sure but idealy by the first of April. I said Ummm? Okay..realizing that he told me this about the 2 or March. A couple days, no biggie. So he pays his rent for the Month of March but then moves out on March 15 th ! That means also that his share of the Gas and Electric bills haven't been paid either and he is now expecting his one months deposit to be returned this week. I am looking into it and from my understanding he has left me with an unrentable space for the next and last few weeks which means I keep the security deposit as he left before the 30 days and I wasn't given sufficient notice to rent the space again. Does anyone know what the law is for this matter ? Does he get his deposit back ? He also left a mess which I have to clean. Thanks....Rich