Mirzo Atadzhanov, 28, had only this to say as he was led out of the 70th Precinct stationhouse in Kensington on Tuesday evening:

Reporter: Why did you do it?

Atadzhanov: I protect myself. I defend myself.

Facing murder and burglary charges in connection with the brutal killing of The New School psychology professor Jeremy Safran.

"It appears at this time that there was in some way a known to relationship between these individuals in the past," NYPD Chief of Detectives Dermot Shea said earlier Tuesday. "Preliminary at this point, but there are reports that the deceased was a professor and the individual in custody may have been a former student."

Safran, 66, was with his wife and daughter at their Ditmas Park home Monday evening. Neighbor Doreen Giuliano said she saw Atadzhanov sitting in his car for three hours, and then saw him enter the side door of the house. That prompted her to text Safran's wife, Jennifer Hunter, and warn her about the intruder.

"She came out, we stood on her lawn, and she said she couldn't find her husband, and she said that was strange because the lights in the basement went out," Giuliano said. "The cops were there in 30 seconds flat. And then they ran in and that's when they found her husband."

Police found Safran lying in the basement with head and body trauma, with a hammer next to him. He was pronounced dead at the scene. Atadzhanov was found hiding in a closet and was taken into custody.

The New School said, in part in a statement, "An internationally renowned psychotherapist, Jeremy was deeply respected and admired by The New School community…We offer our deepest condolences to his family."

"Jeremy was the type of person who would help you shovel the snow, help you take out the garbage. He was the sweetest man," Giuliano said. "And all along while we were talking on the lawn, he was laying on the basement floor."

While it's believed that the victim and the suspect had a previous known relationship, police said Tuesday that the motive remains unknown.