It's often said that the only certainties in life are death and taxes. But you can add "rehashing of the O.J. Simpson case" to that list -- at least for the last 18 years.

So it should come as no surprise that a new book has been published about the 1994 murders of Simpson's ex-wife, Nicole Brown Simpson, and her friend, Ron Goldman.

In 1995, a California jury acquitted O.J. Simpson of the killings. A civil lawsuit, later filed by the victims' families, resulted in a 1997 judgment finding Simpson liable for the deaths and ordering him to pay $33.5 million in damages.

The latest installment in the Simpson library is not another "If I Did It," in which the former gridiron great speculated on how he might have killed his former wife. Instead, the new book points the finger of guilt away from Simpson and lays the blame on his son, Jason Simpson.

"Everything we have in the book is documented. It is not theory or hypothesis. It is fact," renowned private investigator William C. Dear told The Huffington Post about his book, "O.J. Is Innocent and I Can Prove It."

Dear's 576-page "true account," according to Amazon.com, hit the shelves today, retailing at $18 for the hardcover edition.

In the investigation into the murders of Brown and Goldman, Jason Simpson was never considered a suspect or a person of interest. The 41-year-old lives in Miami, where he reportedly works as a chef. HuffPost was unable to reach Simpson for comment Monday because his phone had been disconnected.

But Dear said he has spent nearly two decades looking into the case and assembled a mountain of circumstantial evidence, which, he said, suggests that O.J. Simpson had nothing to do with the murders of Brown and Goldman.

"I flew out two weeks after the murders," he said. "I climbed over the back gate and walked the walkway to the front door, and that's when I realized O.J. could not have done it. But he was there. He was either there at the time or there afterwards [and] became part of the crime."

In his book, Dear claims that he has the knife used in the murders, along with photos and other evidence that suggest the true killer was Jason Simpson, O.J.'s son with his first wife.

"When I tell you we have the weapon -- we found the weapon in Jason's storage facility that he failed to make payments on. We know he carried it -- his initials were carved in the leather sheath," Dear said.

"We have emails from his former roommates that were in college with him. We have our suspect's diaries. We have his forged time card, and we have the vehicle he was driving on the night of the murders," said Dear.

The private investigator also claims to have photos of Jason Simpson wearing the knit cap that was found at the murder scene.

But why? Why would Jason Simpson kill Brown and Goldman?

During O.J. Simpson's trial, prosecutors alleged that the defendant was obsessed with his ex-wife, that he was prone to jealous rages and that he would stalk her.

Dear contends that Jason Simpson has his own demons and suffers from "intermittent rage disorder."

"Our suspect at the time was 5'11" and 235 pounds," Dear said. "He was 24 years old, and he was on probation for assaulting his previous employer with a knife. In addition to that, he's had three attempted suicides and has been in a psychiatric unit."

On the day of the murders -- June 12, 1994 -- O.J. Simpson and Nicole Brown attended a dance recital for their daughter. Dear alleges that Jason Simpson was working as a chef in a Beverly Hills restaurant and had put together a special meal for the family. Brown, however, did not attend.

"You're dealing with a young man who just weeks prior had checked into a hospital where he said he was out of his medication and was about to rage," Dear said. "I have no doubt he had no intention of killing her, but [he] confronted her and, as a result, something happened."

Dear said the diaries he obtained, which were allegedly written by Jason Simpson, refer to the young man's obsession with knives and the problems he was purportedly dealing with.

One entry allegedly reads, "It's the year of the knife for me. I cut away my problems with a knife. Anybody touches my friends -- I will kill them. I'm also tired of being Dr. Jekyll [and] Mr. Hyde."

O.J. Simpson was unavailable for comment at the Lovelock Correctional Center in Lovelock, Nev., where he is serving a 33-year prison sentence. In 2008, he was found guilty of armed robbery and kidnapping for taking sports memorabilia from a dealer at gunpoint.

While the book's bombshell claims have not been proved -- authorities in California have yet to comment on them -- Dear insisted he can back up every allegation.

"I have been inducted into the Police Officer Hall of Fame as a private investigator, so my credentials are not [that of] some idiot guy just throwing it out there. My reputation is important to me. I would not say any of this without a great deal of backup," Dear said.

Dear also contended that he has managed to convince others that his theory has merit.

"I recently did a speech in front of 533 law enforcement investigators and prosecutors," he said. "The first statement I made was 'How many of you believe O.J. was guilty?' and everyone raised their hand. When [my speech] was over, I asked the same thing and only three people voted guilty. So when you get law enforcement and all these people to take that position, that's a pretty strong position."

Loading Slideshow...
  • O.J. Simpson

    O.J. Simpson, 1968. (AP)

  • O.J. Simpson

    Southern California's O.J. Simpson displays an engraved silver case, the Maxwell Award, presented to him in Philadelphia, Jan. 20, 1969, when he was honored as college football's outstanding player of 1968.

  • O.J. Simpson

    Southern Cal's O.J. Simpson poses with the Heisman Trophy at New York's Downtown Athletic Club in this Dec. 5, 1968 photo.

  • O.J. Simpson

    Southern California's O.J. Simpson tries to break a California tackle as he picks up five yards in Los Angeles Memorial Coliseum in this Nov. 9, 1968 file photo. Simpson set the standard for landslide Heisman Trophy victories in 1968.

  • O.J. Simpson

    O.J. Simpson, running back for the Buffalo Bills, posed with his first wife, Marguerite, daughter Arnella, 4, and son Jason, 2, in Buffalo, N.Y., on Oct. 10, 1973.

  • O.J. Simpson

    Football greats Joe Namath, left, and O. J. Simpson, right, stand in front of the Pro Football Hall of Fame in Canton, Ohio, one day before their official induction into the sports shrine, on August 2, 1985. (Mark Duncan, AP)

  • O.J. Simpson

    The five enshrines into the Pro Football Hall of Fame pose with their bronze busts in front of the shrine after induction ceremonies Saturday, Aug. 3, 1985 in Canton, Ohio. O.J. Simpson is second from the right.

  • O.J. Simpson

    American athlete O.J. Simpson ran with the Olympic torch as the crowd cheers in dowtown Los Angeles, Calif., on July 21, 1984, one week before the opening ceremonies of the XXIII Summer Olympic Games.

  • O.J. Simpson

    San Francisco 49ers running back O.J. Simpson is escorted from the field by Atlanta Police after ending his career in the NFL on December 16, 1979, at Atlanta Fulton County Stadium in Atlanta, Ga.

  • O.J. Simpson

    San Francisco 49ers running back O.J. Simpson in 1978. (AP)

  • O.J. Simpson

    Former football star O.J. Simpson and then-friend Nicole Brown get together at party on the night of May 6, 1980, in Beverly Hills. The couple attended the introduction party for the new puzzle branded in America as the "Rubik's Cube."

  • O.J. Simpson

    O.J. Simpson kisses his fiancee, Nicole Brown, at Dodger Stadium during a game against the Cincinnati Reds in August 1980.

  • O.J. Simpson

    O.J. Simpson appears at the Pediatric AIDS Foundation "A Time for Heroes 1994" picnic/carnival in Los Angeles on June 5, 1994. (Donna Gilmartin, AP)

  • O.J. Simpson

    Police tape surrounds the Bundy Drive home of Nicole Brown Simpson, ex-wife of former NFL great O.J. Simpson.

  • O.J. Simpson

    An unidentified police investigator walks past blood-stained towels in the entry way to a Los Angeles condominium belonging to Nicole Brown Simpson, 35-year-old ex-wife of former running back O.J. Simpson.

  • O.J. Simpson

    Blood-stained sheets are strewn along the entryway of the Los Angeles-area condominium of Nicole Brown Simpson Sunday, June 12, 1994, the day after she and Ronald Goldman were murdered there late Saturday night.

  • O.J. Simpson

    This is a 1991 California Department of Motor Vehicles photo of Ronald Lyle Goldman, 26, who was found murdered along with Nicole Brown SImpson on June 12, 1994.

  • O.J. Simpson

    Los Angeles Police Department personnel talk to a handcuffed O.J. Simpson at his home in Los Angeles on June 13, 1994. Just after midnight, Simpson's ex-wife Nicole Brown Simpson and an unidentified man were found dead outside her Los Angeles home. Simpson's attorney showed up and, after talking to police, they removed the handcuffs before taking Simpson for questioning.

  • O.J. Simpson

    Former pro running back O.J. Simpson hangs his head as he sits in his attorney's car on June 13, 1994, after being questioned by Los Angeles Police into the death of his ex-wife, Nicole Brown Simpson. The bodies of the 35-year-old woman and her 26-year-old friend Ronald Goldman, apparent stabbing victims, were discovered after midnight June 12 in her Los Angeles-area home.

  • O.J. Simpson

    A white Ford Bronco, driven by Al Cowlings and carrying O.J. Simpson, is trailed by police cars as it travels on a southern California freeway on June 17, 1994. Cowlings and Simpson led authorities on a chase after Simpson was charged with two counts of murder in the deaths of his ex-wife and her friend.

  • O.J. Simpson

    O.J. Simpson is shown in this file photo with daughter Sydney and son Justin as they arrive at the funeral for his ex-wife Nicole Brown Simpson on June 16, 1994.

  • O.J. Simpson

    This is the booking mug for O.J. Simpson, taken June 17, 1994, after he surrendered to authorities at his Brentwood estate in Los Angeles. Simpson was charged with two counts of murder in connection with the slayings of his ex-wife, Nicole, and her friend Ronald Goldman.

  • O.J. Simpson

    Jurors were shown this Polaroid photo, one of two found in Nicole Simpson's safe-deposit box, during testimony on Feb. 6, 1995, in the O.J. Simpson double murder trial. Older sister Denise Brown testified that she took the pictures a few days after a 1989 beating.

  • O.J. Simpson

    In this June 21, 1995 file photo, O.J. Simpson holds up his hands before the jury after putting on a pair of gloves similar to the infamous bloody gloves during his double-murder trial in Los Angeles.

  • O.J. Simpson

    O.J. Simpson wears gloves as he stands with his wife Nicole on the sidelines of Texas Stadium in Irving, Texas, during the Thanksgiving Day game between the Dallas Cowboys and the Miami Dolphins on Nov. 24, 1993. A prosecutor accused O.J. Simpson of skipping his daily dose of arthritis medicine so his hands would swell, making them too large to fit into gloves linked to murder.

  • O.J. Simpson

    Prosecutor William Hodgman and defense attorney Johnnie Cochran Jr. stand during discussion with Judge Lance Ito at a hearing for O.J. Simpson in Los Angeles on July 29, 1994. Simpson and attorney Robert Shapiro listen.

  • O.J. Simpson

    Former NFL player O.J. Simpson is transferred to the Clark County Detention Center in Las Vegas on Sept. 16, 2007. A prosecutor in Las Vegas said O.J. Simpson "fac[ed] a lot of time" in connection with an alleged armed robbery.

  • O.J. Simpson

    O.J. Simpson appears in a Clark County Justice courtroom for his arraignment in Las Vegas on Sept. 19, 2007.

  • O.J. Simpson

    O.J. Simpson, center, is flanked by his lawyers Yale Galanter, right, and Gabriel Grasso during his arraignment in a Clark County Justice courtroom for his arraignment in Las Vegas.

  • O.J. Simpson

    O.J. Simpson leaves the Clark County Detention Center after he was granted bail in Las Vegas in September 2007.

  • O.J. Simpson

    O.J. Simpson appears in court during his trial in Las Vegas in September 2008. Simpson faces 12 charges, including felony kidnapping, armed robbery and conspiracy.

  • O.J. Simpson

    Room 1203 at the Palace Station Hotel & Casino is seen in Las Vegas. The room is where O.J. Simpson allegedly committed felony kidnapping, armed robbery and conspiracy related to a Sept. 13, 2007 confrontation with sports memorabilia dealers.

  • O.J. Simpson

    O.J. Simpson appears in court during his trial in Las Vegas in September 2008. Simpson faced 12 charges, including felony kidnapping, armed robbery and conspiracy.

  • O.J. Simpson

    In this 2008 file photo, O.J. Simpson is taken into custody after being found guilty on all 12 charges, including felony kidnapping, armed robbery and conspiracy.

  • O.J. Simpson

    O.J. Simpson speaks during his sentencing hearing at the Clark County Regional Justice Center in Las Vegas on Dec. 5, 2008. Sitting right to Simpson is his lawyer Yale Galanter. Simpson was sentenced to at least 15 years in prison for a hotel armed robbery after a judge rejected his apology and said, "It was much more than stupidity."

Also on HuffPost: