They weren't proven innocent by DNA because careful DNA gathering wasn't standard police procedure in 1989, and you don't have to actually penetrate to be convicted of rape in NYC if you're assisting in a rape. The confessions were corroborated with each other and with other witnesses, and one of the confessions was unprompted - one of the boys said, "I had nothing to do with the rape. All I did was feel the woman's tits," without having been told a rape had occurred. Meanwhile, investigators weren't allowed to interview Reyes, nor were other prisoners allowed to talk to investigators about their conversations with Reyes.
Reyes claimed to have raped the victim after the Central Park Five finished with her. Finished doing what? Apparently stripping off her clothes and beating her up and definitely not raping her, although they all said they raped her, and told witnesses at the time they raped her.
Ann Coulter has a blow-by-blow rundown: