Nearly four years after the car-bomb killing of reporter Don Bolles, one of the few certainties in the case is that no one stands convicted of the crime.

That really confronts prosecutors daily here. They have come under increasing criticism over the last three months as the core of their once-carefully constructed prosecution strategy has cracked and splintered.

The courts have overturned convictions of two principal figures in the case and it is uncertain if the state can compel its chief witness to testify at new trials.

Defense attorneys and a local newspaper claim authorities have suppressed evidence and failed to adequately investigate new leads. Don Harris a former county attorney who unsuccessfully resisted attempts by state authorities to remove the case from his jurisdiction in 1976, now says. "I think everybody is going to walk free."

Despite the setbacks. Attorney General Robert Corbin, a Republican who inherited the case when he took state office last year, continues to support the chief state prosecutor, William Schafer III, Schafer and the man who appointed him in 1976, then-Attorney General Bruce Babbitt (a Democrat who went on to become governor), had devised a strategy of gaining convictions of low-level participants in the Bolles murder who then supposedly would implicate others. Corbin now says that strategy "didn't work," but he has not developed a new one. Other theories on the murder, he says, have been carefully examined and rejected.

Bolles was an investigative reporter who had written about organized crime for the Arizona Republic in Phoenix. On June 2, 1976, a bomb exploded under his car in a downtown hotel parking lot. Eleven days later, Bolles died after muttering three words: "Emprise," "Adamson," and "Mafia."

Investigators developed a theory that identified wealthy Arizona rancher and liquor distributor Kemper Marley as the alleged mastermind of the murder plot. Marley, they claimed, was angry at Bolles for several newspaper articles the investigative reporter wrote that cost Marley a seat on the state racing commission.

Prosecutors claimed that Max Dunlap, a Phoenix contractor, who had a lifelong relationship with Marley, and James Robison, a Chandler, Ariz., plumber, played central roles in the killing. Both men were charged and tried together for murder.

Much of the prosecution's scenario was pieced together through interviews with Phoenix tow truck operator John Harvey Adamson, who was arrested hours after Bolles died. Neal Roberts, a Phoenix attorney and former assistant state attorney general, also contributed to the state's case in return for limited immunity from prosecution.

Adamson pleaded guilty to first-degree murder and implicated Dunlap and Robison -- who had no previous criminal records -- in return for a 20-year prison sentence. Marley was never charged because authorities said they could not build a case against him. He denied any role in the murder.

Defense attorneys, however, took their own view of the murder. They claimed Roberts had engineered the killing at the request of the Emprise Corp., a New York-based sports conglomerate with alleged organized crime ties that controlled greyhound dog racing interests in Arizona. Bolles had investigated Emprise, and the defense claimed in court that Roberts and Adamson set up Dunlap to protect other people who could implicate Emprise.

Emprise officials denied any connection with the murder.

The prosecution stategy developed by Babbit and Schafer appeared to be working. It was expected that Dunlap and Robison, convicted and facing potential death sentence, would implicate as many as three others thought to be involved. Babbitt hinted at more arrests.

But Dunlap and Robison steadfastly maintained they were innocent victims of a "get anybody" mentality fueled by Boles' own newspaper and by eager officials hoping to offset a barrage of negative publicity about Arizona's crime problems.

The Bolles murder led to the formation of an investigative reporting team called The Arizona Project. The group, composed of reporters and editors from throughout the country, over several months produced a 23-part nationally distributed series about organized crime in Arizona. The articles led to the formation of a national Investigative Reporters and Editors resource clearinghouse at the Unversity of Missouri.

The prosecutor's stategy was derailed last February when the state supreme court overturned the Dunlap and Robison convictions, ruling that defense attorneys had not been allowed to adequately cross-examine Adamson during the murder trial. New and separate trials were ordered for the two men.

Schafer says that Adamson's testimony is vital to the upcoming trials. But Adamson's attorney, William Feldhacker, says his client has fulfilled terms of the plea bargain. Feldhacker wants a new sentencing deal for additional testimony.

The state responded by filing new first-degree murder charges against Adamson. But there is a legal question whether that constitutes double jeopardy since Adamson has already pleaded guilty to first-degree murder. The state supreme court will decide the question this week.

Meanwhile, a local newspaper, the Scottsdale Daily Progress, has printed more than 100 articles about the case, some of them containing information that suggests racing interests had a role in the Bolles killing -- information that dovetails with the defense attorneys' theories.