(CBS) The father of a murdered CIA agent says he wants to testify at a sentencing hearing that American-born Taliban John Walker Lindh was responsible for the killing.

Johnny Spann, father of Johnny Micheal Spann, said in court papers Monday that he was not consulted about the plea bargain that would give Lindh a maximum 20-year sentence. Spann said he expected at least a life sentence.

Appearing on CBS' "The Early Show" Tuesday, Spann said, "The facts of the case are: he (Lindh) joined the al Qaeda. He fought with the Taliban. That organization had a conspiracy to kill Americans and they did in fact kill."

The sentence likely to be given to Lindh "is not just punishment," Spann argued. "We have people serving more time in prison for dealing drugs than this. We have executed people in the United States for a lot less than what this man has done."

The younger Spann tried to interview an uncooperative Lindh shortly before the government agent was killed in a Nov. 25 prison uprising in Afghanistan.

Lindh pleaded guilty July 15 to contributing services to the Taliban and carrying explosives in commission of a felony. As part of the deal, prosecutors dropped accusations that Lindh participated in the revolt.

"The facts of this case reveal that the defendant had the opportunity to withdraw from the conspiracy and warn my son ... that the prisoners were armed and about to ambush him," Spann's court papers said.

"Because I was never notified that a plea bargain was being considered for the defendant, I had no opportunity for any input in the decision to drop conspiracy charges related to my son's death."

Lindh consistently denied that he had advance knowledge of the uprising.

U.S. District Judge T.S. Ellis III has scheduled an Oct. 4 sentencing hearing for Lindh. Ellis is under no obligation to accept the plea bargain.

"We never thought he would get less than a life sentence," Johnny Spann told CNN. "We just can't stand by and watch this without doing something."