A violent robbery suspect who attempted to hang himself while in police custody in Staten Island Wednesday died of his injuries on Saturday, according to police.

The unidentified 53-year-old was in a cell at the 121 Precinct when officers discovered him unconscious with a sweatshirt around his neck that was attached to his cell, police said.

The man was taken to Richmond County Medical Center where he died three days later, cops said.

Police had the man in custody for an attempted robbery from earlier that day, according to sources.

The suspect had walked into a grocery store at 109 Van Pelt Ave. around 7:30 a.m. and choked a clerk before trying to steal cash from the register, sources said.

Another worker at the store had subdued him until police arrived.