It was no ordinary car accident that took the life of 18-year-old Eric MacLean in March.

Police quickly ruled out speed or alcohol as factors and zeroed in on the defective steering that caused the 1979 Jeep to veer off County Road in Oak Bluffs.

But what really caught their eye was the counterfeit inspection sticker meant to cover up all the mechanical problems.

Six months later, the criminal investigation into the fatal accident has turned up no solid answers, but it has forced one detective to look more deeply at the issue of forged inspection stickers, where they're coming from and how they might shed light on who's to blame for the high school senior's death.

"I know there are other counterfeit stickers out there," state police Sgt. Neal Maciel said last week.

Two weeks ago, Sergeant Maciel arrested Fernando R. Dosreis of Oak Bluffs when he spotted him driving a Geo Metro in Edgartown with a phony sticker. Earlier this summer, Oak Bluffs mechanic Allan (Buddy) deBettencourt pulled a forged sticker off a car he was inspecting.

Sergeant Maciel has found several other fake stickers on Island cars in the last few months, all of them resembling the one that came off the Jeep that crashed in late March. The one from Buddy's Repair matched up exactly with the serial number of the fake sticker on the Jeep.

But even with new pieces of evidence, Sergeant Maciel said he's having a tough time cracking the case. "There's definitely going to be a promising outcome," he said. "But I'm dealing with people who aren't cooperating. They know where they got the stickers from, but this is a five-year felony."

So far, the only people charged in connection with the death of Mr. MacLean are the Jeep's driver, Seamus O'Brien, and the owner, his father, James O'Brien. In May, prosecutors dropped vehicular homicide charges against Seamus O'Brien, a classmate and friend of Mr. MacLean.

But while both men are still facing charges of falsifying a registry document, last spring Seamus O'Brien claimed that his former boss at Beach Road Rentals in Tisbury, Robert Cimeno, put the fake sticker on the Jeep in June 2000 after it failed inspection.

Mr. Cimeno had sold the Jeep to the O'Briens for $3,500, but both Mr. Cimeno and his wife, Patricia, have denied any role in the counterfeit sticker. The Cimenos are named as defendants in a wrongful death lawsuit filed last June by Eric MacLean's mother, Patricia Bergeron.

State police also targeted the Cimenos in their investigation, suspecting them of manufacturing counterfeit stickers. According to an affidavit Sergeant Maciel filed in Edgartown District Court, police suspected that the Cimenos' son, Jeffrey Cimeno, who owns Patti's Taxis, was forging stickers to use on his cabs and one of his own cars, a 1994 Toyota.

Details in the affidavits looked convincing. Two of the cabs had no record of ever being inspected. And two witnesses told police that they had seen one of the cabs at the Steamship Authority terminal in Vineyard Haven with an inspection sticker whose serial number matched the one from the Jeep.

But even after raiding Jeffrey Cimeno's home and the business on Beach Road in June, police made no arrests charging anyone with falsifying registry documents.

The trail seemed to go cold, and Mr. MacLean's family members looked for signs of progress. "It's very frustrating," said Paula O'Connor, the MacLean family spokesman. "Making headway in the criminal case would help the family to heal."

But a new development holds some hope. Last spring, police traced the serial number from the Jeep's inspection sticker back to a VW Jetta inspected in the Boston suburb of Somerville.

As it turns out, Somerville could be a nexus of counterfeit inspection stickers and the potential source of stickers ending up on the Island. Somerville police, led by officer Robert Hickey, have issued 97 citations this year for forged stickers.

Sergeant Maciel has not yet talked with Somerville police, but he's hoping to find connections. "There's a pocket of forged stickers coming out of Boston," he said. "And there's a good possibility they match up [with the Jeep's sticker]. This investigation is not closed."

When state police questioned Mr. Dosreis about the fake sticker on his Geo, he told them, through an interpreter, that he bought the car and got his inspection sticker in Boston. He would not say where he obtained the sticker.

Island police, he said, need better training in spotting a fake. Mr. deBettencourt, who deals with stickers every day, already knows the finer points. The counterfeits, he said, have square edges, not curved like the real ones, and the numbers are bigger.

"The level of sophistication has been here just in recent years," said Sergeant Maciel. "In my career, it's always been a green piece of paper, people taking a six and trying to make it an eight. But in this era now, they're made on a computer and geared toward the individual vehicle."

Forged inspection stickers may be a clever way to beat the system, avoiding the lines and the cost of repairs, but the public safety ramifications are great.

"When you've got a vehicle on the road that wouldn't be there if it weren't for a fake document, that's a huge issue," said Sergeant Maciel. "Because of the fatality, there's a new focus. That Jeep should never have been on the road."