There are some crimes that are too heinous even for convicted murderer, rapist and thief Russell Williams to admit to, according to a new book that reveals previously unknown details about the investigation into the former colonel's crimes.

According to the book "A New Kind of Monster", investigators found child pornography on Williams' computer, but the former commander of the CFB Trenton air base wasn't willing to own up to it. The Random House Canada book, by Globe and Mail crime reporter Timothy Appleby, is due to hit bookshelves mid-April.

The book claims that Williams was willing to plead guilty to all the other charges against him, including rape, murder and countless bizarre home invasions and the theft of hundreds of pieces of women's underwear and sex toys.

But the guilty pleas would be offered as a trade-off.

"He was not willing to acknowledge downloading child pornography from the Internet, and during the pretrial negotiations he'd been adamant: child porn charges would be a deal-breaker," the book reveals.

"If they were laid, there would be no guilty pleas on the murder and sexual assault charges. Instead, everything would go to trial -- an outcome that neither the prosecution nor the defense was eager to force."

It wasn't that the additional charges would make a difference to his sentence -- he was already facing the certainty of life behind bars. But "because it would be too disgraceful," the book suggests.

Appleby, who cites a source who took part in the proceedings, wrote in the book that the images found on Williams' computer were "not absolutely the worst of its kind," but that it was "pretty loathsome stuff all the same, and very clearly illegal."

The book suggests that Williams could justify murder, and even rape, as acceptable actions that take place within the realm of the military or in time of war. But the sexual abuse of children, the source told Appleby, was considered unacceptable and shameful under any circumstances.

In the book, Appleby argues that Williams' refusal to acknowledge possessing the child pornography is evidence that he knew right from wrong.

Williams, pleaded guilty in October to two counts of first-degree murder, two counts each of sexual assault and forcible confinement, and 82 break and enters that date back to 2007.

Williams, the former commander of Canada's largest military airfield, faces life in prison with no chance of parole for 25 years.