A mentally ill Harlem man has been arrested and charged with fatally stabbing his mother, critically stabbing his brother, and setting their apartment on fire yesterday. Cops say 31-year-old David Elias stabbed his 55-year-old mother, Ruth Montano, multiple times in the torso, then set fire to her East Harlem apartment around 4:25 p.m. Saturday. Elias also is accused of stabbing his 32-year-old brother in the torso and head in the apartment. "She was just lying there lifeless," neighbor Marian Garcia, who saw Montano face-up in the hallway outside her 10th-floor apartment, told the News. "She wasn't saying anything and her eyes were closed."

Neighbor Anthony Watts, 16, ran into the burning apartment and pulled Montano out after he heard screams and someone had thrown a shoe out the window to get help. "I saw the woman on the floor and I dragged her out," Watts told the News. "She had a pulse, but she wasn't breathing. When I got there, [the suspect] was crying over the body and saying something in Spanish," he added. Watts told the Post when he asked Elias what happened, he responded: “You’ll understand. You’ll know what I’m talking about.”

it's unclear what prompted the attack. Elias' brother is currently at Harlem Hospital in critical condition. Elias has been charged with murder, attempted murder and arson.