Published: Oct 13, 2010 3:26 PM EDT
Updated: Oct 13, 2010 12:26 PM EDT

MIAMI, Fla. (AP) - A Florida inmate has pleaded guilty to taking part in a 1989 fatal robbery.

Miami-Dade prosecutors say 37-year-old James Rich pleaded guilty to second-degree murder on Tuesday. As part of a plea deal, he will receive 15 years, on top of a life term he's already serving for an unrelated armed burglary in Broward County.

In November 1989, a robber shot gas station clerk Alberto Roque with a shotgun. Rich, who was already in prison, contacted prosecutors in 2007, saying he had information about the killing. He confessed to being a lookout for the robbery.

Investigators are still building a case against a second suspect, who is already in prison on unrelated charges.

It's still not clear who actually killed the clerk.