Osborn had a massive heart attack on Friday and died shortly before 1 a.m. Sunday, attorney Joe Cheshire said.
Osborn represented Reade Seligmann, one of three Duke lacrosse players charged in the case stemming from a dancer's allegation she was sexually assaulted at a team party. The players were originally indicted on charges of rape, sexual offense and kidnapping, but Durham District Attorney Mike Nifong dropped the rape charges in December after the accuser changed a key detail in her story.
All three have steadfastly maintained their innocence.
"We will never forget Kirk and his sacrifices for Reade and for justice," Seligmann's family said in a statement. "Kirk's fight for the truth and for justice in this case met the highest standards of ethics and professionalism and stand in stark contrast to those who condemned Reade. He is an example of what a lawyer should be."
Actions by Osborn in the case included a motion with phone records and security camera images showing Seligmann would have been nearly a mile away from the Durham house at the time the woman said he was taking part in the attack.
Osborn also filed a motion to have Nifong removed from the case, arguing that Nifong went after the lacrosse players to win votes.
In January, Nifong asked the state attorney general's office to take over the investigation after the state bar charged Nifong with several ethics violations tied to his conduct in the lacrosse case. If convicted of the ethics violations, Nifong could be disbarred.