Fifty-year-old Sergey Mamontov of 3395 Nostrand Avenue in Sheepshead Bay has confessed to dismembering his roommate because, he felt, “there was no other way to take care of [the victim],” police sources told the Daily News. Mamontov had squabbled about noisiness and partying with his 55-year-old roommate Aleksandr Zilbergleyt, who had been living there for about eight months. A person living in the building reported hearing a loud crashing sound on March 25, the day Zilbergleyt disappeared. “He was very meticulous, very methodical,” a source told the Daily News. “He cleaned up afterwards. He put the body parts in the refrigerator … He didn’t know what his next move was.” Police found Mamontov watching TV when they arrived at the residence.