D.O. Cannons (real name Gerard Fields) was a 26 year old rapper who gunned down on 4 September 2003. He was part of Murder Inc. Records and appeared on the Ja Rule album "Blood in My Eye". He dissed 50 Cent because of his association with Ja Rule and many suspect that he was killed because of it. One of 50 Cents non-rapping members of G Unit was killed within a week of Cannon's death. Wikipedia
The definitive Wikipedia entry for D.O. Cannons. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/D%2eO%2e_Cannons