A teen was busted in the fatal shooting of an autistic man during a botched robbery at a Bronx park — as his grieving sister revealed new details of his tragic final hours.

Luis Castillo, 19, was hit with murder and related charges Monday more than a month after his alleged accomplice, Axel Martinez, 20 was captured by cops in connection with the slaying of 26-year-old Ronell Marte last month, according to authorities.

Marte was shot in the chest inside the Starlight Park along East 174th Street around 2:50 a.m. on Sept. 4 and was later found by a biker lying in a pool of vomit and blood, police and law enforcement sources said.

Luis Castillo, 19, was arrested in connection with the fatal shooting of Ronell Marte, 26, an autistic man, during a botched robbery at Starlight Park that

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