FAIRBANKS -- The Tanana Chiefs Conference has increased its reward for information about the 1997 killing of John Hartman.

The Fairbanks Daily News-Miner says the conference is trying to exonerate the four men convicted of his murder. TCC is offering a reward of up to $35,000 for information that will help free Marvin Roberts, Eugene Vent, George Frese and Kevin Pease.

The four men were convicted in 1999 of killing Hartman and are serving sentences of 33 to 79 years in a Colorado prison. Many members of Fairbanks' Alaska Native community insist the four were wrongfully accused.

Hartman was 15 years old when he was found beaten and stomped in downtown Fairbanks. He died at Fairbanks Memorial Hospital after lingering in a coma.