Robin was murdered by the Riddler.
As revealed in Batman: Legends of the Dark Knight #185-189, the Riddler is stripped of his deductive powers and left to rot as a member of Gotham City's vast and invisible homeless population
 However, Batman and Dredd are able to work together to overcome their opponents, culminating in Dredd shooting Riddler in the shoulder and Batman claiming the device, subsequently using it to return the survivors home

