PALM DESERT, Calif. -

Personal attacks heated up on the campaign trail on Thursday as U.S. Rep. Mary Bono Mack's campaign held a news conference releasing an audio tape of her challenger, Democrat Dr. Raul Ruiz, reading a letter of support for activist Leonard Peltier at a Thanksgiving protest reportedly held in 1999.

Peltier is a Native American found guilty of killing two FBI agents in 1975. He is now serving a life sentence in prison. The letter was written to Peltier by Subcommandante Marcos, the spokesman for the Zapatista Army of National Liberation.

Ruiz, while in medical school, is heard reading, "If Leonard Peltier is guilty, then we are all guilty, because we seek out history. On his shoulders we fight for a better place in the world."

Dr. Ruiz spoke at an event in Palm Springs on Thursday, shortly after Bono Mack's campaign press conference, and claimed he simply didn't remember reading the letter.

"Yes, that's absolutely true. I did not remember reading any letter until now that they have this audio recording," he said.

"I think this is shocking and appalling. The man, who's asking for votes of the 36th District, would deceive them, would lie to them. And say, ‘I don't recall such a letter,’" said Bono Mack's campaign director Marc Troast.

Dr. Ruiz added he doesn't support Peltier now and it's the current issues that matter.

"During this entire time (Bono Mack) continues to talk about something that occurred when I was a student and not talk about how we're going to get people jobs, the economy and healthcare," said Ruiz.

In wake of the recent campaign attacks, members of the Agua Caliente Band of Cahuilla Indians are stepping in. They said the following statement written by Tribal Chairman Jeff Grubbe would “speak for itself.”

“For these reasons, we were offended that Bono Mack described past protests by her opponent on behalf of Native Americans as 'radical' and 'anti-American.' This is an outrageous and unacceptable insult to all Native Americans, including those who live in the district she represents here in the Coachella Valley," said Grubbe.

Bono Mack’s campaign spokesman Jim Specht responded to the tribe’s statement saying, "They may see this in one direction, but she has never seen this as any attack on Indian traditions or history." 

"Even her own constituents, the Agua Caliente is condemning the fact she is coming down and making this her focal issue," said Ruiz.

The tribe says it is not endorsing either candidate in the newly formatted 36th Congressional District.