WASHINGTON (CNN) -- The case of a convicted rapist paroled in 1999 has come back to haunt Republican presidential candidate Mike Huckabee, with the mother of a woman the convict later murdered pledging to campaign against the former Arkansas governor.

Mike Huckabee says he did not try to influence the Arkansas Parole board to parole Wayne DuMond.

Huckabee, during his first term as Arkansas governor, expressed support for the parole of Wayne DuMond in a letter to him.

DuMond was serving a life sentence for raping a 17-year-old girl. The Arkansas parole board had the final say on DuMond's parole.

Less than a year after his release from prison in 1999, DuMond was accused of raping and murdering Carol Shields, a woman in Kansas City, Missouri. DuMond was convicted of the crime in 2003. He died in prison in 2005.

Huckabee on Sunday confirmed to CNN he had sent the letter to DuMond.

The murdered woman's mother, Lois Davidson, said she will "absolutely campaign against" Huckabee, and said she decided to come forward when he started doing well in the polls.

"It's because he is a serious contender," Davidson said. "I didn't think he had a chance, but now he's right up there in Iowa."

In an interview with CNN Wednesday, Huckabee said it was "heartbreaking" that the murders had become politicized.

"There are families who are truly, understandably and reasonably, grief stricken," Huckabee said. "And for people to now politicize these deaths and to try to make a political case out of it rather than to simply understand that a system failed and that we ought to extend our grief and heartfelt sorrow to these families, I just regret politics is reduced to that."

Huckabee said he had considered granting DuMond clemency, but he dropped the idea in response to public outcry.

Huckabee also said he did not grant clemency because he wanted to ensure DuMond was supervised when he was released from prison.

"Had I granted his commutation, then there would have been no supervision at all," Huckabee said, "I wasn't comfortable with that."

The DuMond case began in 1985, when he was accused of raping a 17-year-old girl. Before trial, DuMond was attacked in his home and castrated, and the local sheriff kept the severed testicles in a jar. No charges were brought in the attack.

Huckabee said the process leading to DuMond's release began under former President Bill Clinton when he was governor of Arkansas.

Clinton and, later, Arkansas Gov. Jim Guy Tucker commuted part of DuMond's sentence, Huckabee said, because they thought it was excessive.

When he spoke about the case, Huckabee suggested his role in the decision to parole DuMond was limited.

Huckabee said it was the decision by Clinton and Tucker that made DuMond eligible for parole, and Huckabee declined to reduce DuMond's sentence further.

In 1996, Huckabee sent a letter to DuMond saying parole was the best option for him, the National Review reported.

"I've never made a decision about the DuMond case other than the decision to write the letter" to DuMond, Huckabee said. "That was my decision, but I didn't parole him, because governors don't parole people in Arkansas."

However, Charles Chastain, a parole board member at the time, told ABC News he felt pressure from Huckabee when the board considered DuMond's parole in 1996.

The Arkansas Times reported in 2002 that two other board members said they were influenced by Huckabee to parole DuMond.

Huckabee denied he asked the board to approve DuMond's parole.

"No, I did not," Huckabee said Sunday. "Let me categorically say I did not."

Huckabee said Wednesday his discussion with the parole board in 1996 was a general discussion about clemency, not about the DuMond case.

Huckabee noted that the three board members who said they were pressured were appointed to the board by Democrats Clinton and Tucker.

Documents posted on the Web site The Huffington Post indicate Huckabee received letters from several victims of DuMond before his release.

The letters detailed his past actions and pleaded that he remain incarcerated.

"I feel that if he is released it is only a matter of time before he commits another crime and fear that he will not leave a witness to testify against him the next time," one victim wrote. She described how DuMond had raped her at knifepoint.

A former top Huckabee aide confirmed to CNN the then-governor received that letter and a follow-up phone call from the victim.

In another letter, a woman documented how her mother was raped by DuMond, and said he had told her mother he would rape her daughter if she did not cooperate.

The Huffington Post said it received the never-before-published letters from a "deeply troubled" former aide to Huckabee who believes the presidential candidate has "deliberately attempted to cover up his knowledge of DuMond's other sexual assaults."

Huckabee spokeswoman Alice Stewart denied to the Huffington Post that Huckabee received any of the letters, but later told CNN he got at least one from a victim named "Onita," who lived in DeWitt, Arkansas.

It's not clear if this is one of the letters posted on the Huffington Post, because the site has redacted the names.

The Huffington Post has published three victims' letters, and says it will post additional files later Wednesday. E-mail to a friend

CNN's Dana Bash and Alexander Mooney contributed to this report.

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