In court papers, the prosecutors identify Ronald "Tenad" Washington as the armed accomplice of a second unidentified gunman who shot Jay, whose real name was Jason Mizell, inside his New York recording studio in 2002. They say Washington also is a suspect in the 1995 fatal shooting of Randy Walker, a close associate of the late rapper Tupac Shakur.
The papers were filed earlier this month in the federal trial of Washington, who was convicted in a string of armed robberies that occurred just after Jay was killed. Prosecutors declined on Tuesday to discuss the unsolved slayings.
A Mizell family spokeswoman welcomed news that authorities had for the first time publicly identified a suspect.
"We're relieved there's some information coming out, although we understand that it's not the full story," said the spokeswoman, Fern Yates.
Washington, 45, has denied any connection to either the Mizell or Walker cases. In a sworn statement, he claimed hostile detectives had hounded him about the slaying of his "childhood friend" Mizell and other crimes.
Washington's criminal record dates to 1982, and includes convictions for assault, drugs and grand larceny, authorities said.
During the 1980s, Mizell made rap music history working the turntables as Joe "Run" Simmons and Darryl "DMC" McDaniels rapped on hits like "King of Rock," "It's Tricky" and a top-40 remake of Aerosmith's "Walk This Way."
Mizell was gunned down Oct. 30, 2002, at his 24/7 recording studio. According to a performer there, a man wearing a black sweat suit appeared, embraced Mizell, pulled out a .40-caliber pistol and opened fire.
A first round missed Mizell and injured another person. A second bullet, this one fired from point-blank range, entered the left side of Mizell's head. The shooter vanished.
For his part, Washington "pointed his gun at those present in the studio, ordered them to get on the ground and provided cover for his associate to shoot and kill Jason Mizell," prosecutors said in court papers.
While being sought for questioning in the Mizell case, Washington fled and lived in various motels, authorities said. He held up several fast-food restaurants and other businesses with a pellet gun before his arrest in December 2002.
Prosecutors claim Washington was among three men involved in a fatal car chase with another hip-hop figure Walker on Nov. 30, 1995. The suspect allegedly fired a gun out a car window, killing Walker and causing his minivan to crash.
Walker had performed with the group Live Squad under the name Stretch. He also was known for producing several songs for Shakur, victim of an unsolved murder in 1996 in Las Vegas.