NEW YORK - The suicidal ex-boyfriend of a California college student killed her by strangling her and smothering her face with a towel after an argument inside a New York University apartment, authorities said Wednesday.

The boyfriend, Michael Cordero, 23, remained hospitalized and under suicide watch after slitting his wrists on Tuesday night shortly before his capture. Prosecutors said once released from the hospital, he would be arraigned on second-degree murder charges; they didn't know if he had an attorney.

When medical staff asked Cordero about his self-inflicted wounds, he told them, “I tried to kill myself because I killed my girlfriend,” police said.

He later offered detectives a detailed account, telling them he had argued with Boitumelo McCallum inside the Greenwich Village apartment owned by her mother, an NYU professor, on Friday before killing her, police said.

The medical examiner ruled Wednesday that McCallum died from “manual strangulation and smothering due to covering of face with a towel.” The conclusion was consistent with Cordero's confession, said New York Police Department spokesman Paul Browne.

The badly decomposed body of McCallum, 20, was found wrapped in a sheet in the locked bedroom of the apartment on Sunday after tenants noticed a foul smell. Police officers entering an unlocked balcony window discovered her on the floor between the bed and a wall.