Michael Fortier, the government's key witness in the Oklahoma City bombing trials will appeal his 12-year prison sentence on the grounds that the penalty was based on false claims, his attorney said.

Fortier, who testified against Timothy McVeigh and Terry Nichols, was sentenced last month after pleading guilty to failing to notify authorities about the bombing plot, transporting stolen weapons and lying to FBI agents.Prosecutors never proved Fortier knew the money he earned by selling stolen guns would be used for the bomb plot. But U.S. District Judge Thomas Van Bebber ruled that Fortier facilitated the deadly conspiracy by giving McVeigh part of the profits.

The ruling allowed the judge to consider a maximum sentence of 23 years instead of the three-year term recommended in guidelines for a conviction on transporting firearms, defense attorney Michael McGuire said.

In a notice filed Wednesday with the 10th U.S. Circuit Court of Appeals, McGuire listed nine issues he plans to raise on appeal, including an argument that Van Bebber should have given more weight to Fortier's cooperation and remorse.