LYNN – A leading member of a notorious Lynn gang was sentenced to 15 years in federal prison last week for conspiracy to sell crack cocaine, authorities said.Donald Oliver Jr., 23, of 85 Timson St., was indicted along with 16 other members of the Deuce Boyz and Soldiers gangs one year ago in a local, state and federal gang crackdown.Oliver was named as “a leader of the Deuce Boyz/Soldiers” in an FBI court affidavit.A federal grand jury indicted Oliver for conspiracy to distribute cocaine and charges of distribution of crack cocaine in April 2007.Authorities say Oliver arranged for two undercover witnesses to purchase two handguns and two “eight-balls” of crack cocaine from Nelson Sanchez, 19 and Christopher Gutierrez, 22, of Lynn, on March 1, 2007 on Lafayette Park in Lynn. Gutierrez and Sanchez allegedly robbed the witnesses at gunpoint as the incident was captured on a secret FBI video surveillance tape.Sanchez pleaded guilty to armed robbery and weapons charges in Salem Superior Court in January and was sentenced to 10 years in prison followed by five years of probation.Before the final transaction went down, Oliver allegedly sold the informants 75 grams of crack cocaine while he was on pre-trial release for selling over 100 grams of crack, along with various drugs and weapons charges.Within days of Oliver’s arrest, officers at the Middleton House of Correction confiscated his prison jumpsuit because he decorated it with gang graffiti, according to the affidavit. He also decorated the walls of his jail cell with gang emblems and wrote the word “snitch” next to the name of an undercover informant, the affidavit said.Authorities say Oliver, along with several other gang members, were allegedly involved in the February 2005 shooting death of July Gratereau, 18, of Salem. Gratereau slept with Sanchez’s girlfriend shortly before he was killed in a robbery, according to authorities.The indictments of Oliver and 16 other alleged gang members was the result of a six-month investigation and announced during a press conference at the Moakley Federal Courthouse in Boston on May 2, 2007.At the announcement, authorities displayed items seized from the defendants, including $38,000 cash, crack cocaine, a sawed-off shotgun, a rifle and a Tec-9.Also indicted were David M. Valentin who is currently a fugitive, Clifford Slaughter, 31, of 14 Merill Ave. #3, Frank Puello, 23, of 133 Kimball St., Revere, Loeki Rodriguez, 35, of 526 Western Ave., Orlando Vales, 21, of 1704 Broughton Drive, Beverly, Rafael Cristobal, 24, of 17 Highland Ave., Adonis Cristobal, 24, of 36 Rantoul Ave., Manuel Bisono, 29, of 205 Highland Ave., Salem, Daryl Knight, 22, of 137 Broad St., Falkosky Beltre, Theodore Allen, 22, of 42 Melvin Ave., Carlos Hunter, 23, of 35 Laighton St., Saul Rodriguez, 25, of 78 Harwood St., an unidentified juvenile, Sanchez, of 35 Timson St. and Gutierrez, of Lynn, exact address unknown.