NEW YORK -- A 17-year-old boy accused of throwing a 9-year-old boy off the roof of a Bronx apartment building pleaded not guilty Sunday.

Nine-year-old Freddy Martin was found Friday night on the pavement unconscious with severe body trauma in front of the five-story building on Nelson Avenue in Morris Heights. He was taken to Columbia Presbyterian Hospital where he remains in critical condition.

On Saturday, police arrested his neighbor, 17-year-old Casmine Aska, who originally told investigators that he threw Martin off the roof after they got into a fight, a police source said. The boys are not related, but live in the same building.

But according to court documents, Aska now says he grabbed the boy by the legs and then slipped, causing Martin to fall.

Aska was arraigned Sunday on attempted murder, assault and reckless endangerment charges.