Highway robberies such as the one that took the life of Dr. Gulam Moonda are among the rarest of crimes.

Alfred Blumstein, a criminologist and professor at Carnegie Mellon University, said they usually fall into two categories -- random attacks and murder conspiracies disguised as random attacks.

Comedian Bill Cosby's only son, Ennis, died in one of the nation's most publicized roadside robberies. Cosby, 27, had the bad luck to get a flat tire on a dark Los Angeles freeway. Along came a thief who spotted him and his $130,000 Mercedes-Benz.

"Here was a young African-American guy with a flashy car, so the robber assumed he had to be a drug dealer with a lot of money," Blumstein said.

The thief, a Ukrainian immigrant with gang ties, shot Cosby in the head, purportedly because he did not surrender his money fast enough.

Investigators solved Cosby's 1997 murder in two months. Tips leading to the killer were generated with the help of a $400,000 reward, funded mostly by two supermarket tabloids.

Blumstein said the counterexample to Cosby's random killing is the staged highway robbery, in which conspirators try to conceal a murder plot.

One such case, the shooting death of Maria Marshall on the Garden State Parkway in New Jersey, became one of the most famous crimes of the 1980s.

Marshall, 42, was riding home from an Atlantic City, N.J., casino with her husband, Rob, a successful insurance salesman and campaign organizer for the United Way in Toms River, N.J.

He said he felt a tire going flat, so he pulled into a darkened picnic area to check it. There, Rob Marshall said, somebody struck him from behind and knocked him out. The attacker spared his life, but killed Maria Marshall with two bullets to the back.

Police instantly doubted Marshall's account of a robber committing the crime. They thought the shooting looked like the work of a professional killer, not a panicky thief.

The gunman took Maria Marshall's purse, but did not steal her jewelry. Plus, the tire Rob Marshall said was going flat appeared to have been slit with a knife after the car had stopped.

Investigators soon discovered that Rob Marshall was having an extramarital affair, that he was $334,000 in debt and that he had taken out $1.5 million in life insurance on his wife. The last $100,000 policy was purchased a day before her death Sept. 7, 1984.

Jurors convicted Marshall in 1986 of arranging his wife's murder. They sentenced him to death.

By then, two of the Marshalls' three sons also believed him guilty. Their story was detailed in Joe McGinniss' best-seller "Blind Faith," which became a television miniseries.

Rob Marshall, now 65, sits in the New Jersey State Penitentiary, where he continues to insist that he had nothing to do with his wife's murder. His youngest son, John, continues to support him.

After 18 years of appeals, Marshall succeeded in having his sentence reduced from death to life. The state is appealing that ruling.

Though Marshall was convicted, whoever fired the shots that killed his wife got away with murder. Prosecutors accused a Louisiana man, Larry N. Thompson, of being the triggerman. The same jurors who found Marshall guilty acquitted Thompson.

Two other Louisianans went to prison for conspiring with Marshall in his wife's murder. Marshall had made various cash payments to one, and he placed more than 30 phone calls to the other in the weeks before the murder.

Blumstein said Moonda's death May 13 on the Ohio Turnpike bears numerous similarities to the Marshall case.

"It certainly sounds like more than a robbery," he said.

The Ohio State Highway Patrol has taken a similar position, saying robbery may not have been the reason for Moonda's killing.

A millionaire urologist from Sharpsville, Mercer County, Moonda was traveling with his wife, Donna, and mother-in-law to Toledo. Donna Moonda stopped their car on the turnpike about 15 minutes south of Cleveland. She said her husband was to take over the driving.

Just then, a robber approached Gulam Moonda, 69, stole his money and shot him in the face. Donna Moonda, 46, told police she saw the gunman but could not identify him, nor did she notice the license plate of the dark van he fled in.

The killer shot Moonda in daylight, about 6:30 p.m. Then he had to escape the turnpike by driving through a tollbooth, knowing he had left two witnesses alive.

Members of the highway patrol and Ohio Turnpike administration said they could not remember any crime similar to the attack on Moonda. The 241-mile turnpike opened 50 years ago.

As part of its investigation, the patrol is delving into Moonda's financial assets and his wife's background. She is on probation for stealing painkillers from the hospital where she worked as a nurse anesthetist. Police say she also was in a relationship with Damian Bradford, 23, of Center. They met in a drug rehabilitation program.

Police call Bradford "a person of interest" in Moonda's death.