Jonathan Pena Castillo called his doomed ex at all hours of the night and would show up unannounced at the family's Inwood apartment before he stabbed her to death on the sidewalk outside her house, her brother, Ronny Peralta, 27, said.
His obsession drove Edith Rojas, 19, a medical assistance student at Bronx Community College, to dump him about 8 months ago -- but the jilted man wouldn't give up, he said.
"She told my mom ... that he had problems, like he was a possessive guy," he said. "He wanted to be always calling her, always harassing her. He didn't want her to be with nobody else. Not hanging out with nobody else, calling at all times of the night."
But the calls and visits continued, even after they broke up.
"He thought that she was with somebody else. So he kept showing up around," Peralta said of Castillo, who lives in New Jersey.
After allegedly stabbing Rojas, a crowd of neighbors ran down to the street and found the woman dying in the arms of her wailing mother. Castillo watched her bleed on the sidewalk, Peralta said.
"As soon as we came downstairs, [Castillo] was just standing, facing her, watching her die. Since we recognized him, he started running. Everybody started chasing him,” he said. “People with dolls, they threw the dolls at him. He went to the park and he disappeared."
"As soon as he ran to the park, he went into hiding. He just laid down in the middle of the park by the fountains. By the time I got there, he already stabbed himself."
Castillo was in custody at St. Luke's Hospital in a medically induced coma, police sources said.