DELTONA, FLA. ? The key prosecution witness in the deaths of six people in what prosecutors say was a dispute over a video game system claimed innocence Thursday and refused to testify.

Robert A. Cannon, 20, said he wanted to withdraw the guilty plea he had entered in October in a deal to spare him a possible death penalty.

After offering sympathy to the victims’ families, Cannon turned to the judge and said, “I am not guilty, sir.”

Cannon had earlier admitted to taking part in the six clubbings and stabbings in a Deltona home in August 2004 and faced a life sentence as part of the plea deal. Prosecutors say a former prison inmate, Troy Victorino, led the violence in revenge because one of the victims had cleared Victorino’s Xbox video game system and some clothing out of her grandparents’ vacant home, where he had been temporarily living.