Melvin White

Melvin White's fingerprints were on the bullets fired during the shooting murders of Patrick Harvey and Richard Dent.

Biography
Melvin White was convicted of aggravated assault, and moved to Arkham Asylum twice. He was either released, or escaped during Ras al Ghul's assault on Gotham City.

After White's fingerprints were discovered on bullets fired at Patrick Harvey and Richard Dent, Bruce Wayne searched for him from an MCU convict database.

Wayne pursued the lead, and discovered Gotham City Honor Guards tied up in Melvin White's apartment during the memorial of Commissioner Loeb.

Behind the scenes

 * Some believe this concluded that the Joker was Melvin White, when nothing stated that he was the shooter. Also, the GCPD could not identify the Joker's finger prints but Batman found Melvin's finger prints from the GCPD database, so Batman would likely be no more successful from hacking their database.
 * Melvin White had been convicted of aggravated assault and moved to Arkham twice, so unless he had self-inflicted or received the scars after his release/escape, employees from Arkham would have recognized the Joker.
 * The MCU had Melvin White in their database, which likely included them taking White's fingerprints, blood samples, and dental records, all of which could not be found for the Joker.
 * A possible scenario involving the murders of Patrick Harvey and Richard Dent may be that the Joker had Melvin White load the bullets into a gun, while the Joker pulled the trigger, personally killing them.
 * Similarly, Melvin White may have handled the bullets, while the Joker could have loaded and fired them with gloved hands, leaving none of his own fingerprints on them.