LAWNSIDE — Two years ago on a darkened stretch of South Jersey highway, Clayton Tanksley was almost killed when his SUV was rammed from behind and sent tumbling to the side of the road — by a man who doesn't exist.

"He hit me hard enough to crush the back of the car like an accordion," said Tanksley, 46. "It was like a shark attack. It’s so sudden, out of the blue."

The accident, on Route 295 in Camden County, left Tanksley with a demolished car, back problems and recurring flashbacks.

"In the middle of night, everything is calm and peaceful," Tanksley said. "And then you live through it again. Even the smells."

According to the State Police crash report, a man named William Gillespie was behind the wheel of the other car that night. As Tanksley’s medical bills from the crash neared $30,000, his lawyer filed a lawsuit against Gillespie.

But when it came time to serve him, Gillespie was nowhere to be found. A private investigator couldn’t find Gillespie at the home or business listed on the State Police report of the accident, and the insurance company named did not recognize the information about his car.

It was as if Gillespie didn’t exist, and for good reason — he doesn’t.

Through a series of interviews and a trail of documents, The Star-Ledger has learned that Gillespie is the undercover name for State Police Detective Sgt. William Billingham and that his true identity was withheld from Tanksley — in violation of State Police policy — leaving Tanksley and his lawyer to go on a prolonged wild goose chase for a phantom. The newspaper also found that Billingham's fellow troopers provided Tanksley's insurance company with fictional and incomplete information.

In fact, Tanksley — an actor who has appeared in movies and on television in "The Cosby Show" under the name Clayton Prince — had no idea who really hit him until The Star-Ledger tracked him to his Philadelphia home in April.

Tanksley’s lawyers are considering a lawsuit against the state claiming his civil rights were violated.

"It looks like a cover-up," attorney Charles Nugent said. "There’s no innocent explanation for it, as far as I’m concerned."

Questioned outside his South Jersey home Saturday, Billingham would say only that his lawyer had instructed him not to comment on the case.

IN THE DARK

While Billingham’s identity was a secret to the man he could have killed, memos between ranking State Police officers show that trooper brass were well-informed about the crash. So were prosecutors: Billingham, an 18-year veteran of the division, has been the subject of internal and criminal investigations into the accident, but they have inched their way through the legal system.

He eventually was suspended without pay and charged with assault by auto on March 4 — two years after the crash — and prosecutors say there’s evidence he was drunk behind the wheel. His lawyer, Steven Secare, declined to comment on the allegations except to say Billingham is pleading not guilty.

Tanksley and his lawyers were unaware of any inquiry until they were told by The Star-Ledger.

"No one told me there was any investigation," he said.

Two sources said state investigators are also probing the way troopers responded to the predawn crash, starting with the undercover name on the crash report, obtained by the newspaper.

The troopers wrote in their report that Billingham, 51, was not tested for alcohol. There were no charges filed or tickets issued, according to the report and motor vehicle records.

Details of the accident — including that Billingham was off-duty and driving an unmarked troop car — were forwarded to superior officers, including State Police Superintendent Rick Fuentes. But sources said the accident might never have been examined if not for an anonymous letter alerting the Attorney General’s Office to the conduct of Billingham and the other troopers who protected him.

The criminal case against Billingham is now being handled by the Ocean County Prosecutor’s Office, but it didn’t arrive there until almost a year after the crash. (Camden County authorities passed on the case to avoid the appearance of a conflict of interest because Billingham’s brother is the sheriff there.)

It was another year before Billingham was charged. By that time, the statute of limitations rendered it too late to file a charge of driving under the influence. The State Police say they will not comment because the case is still under investigation. Pressed by The Star-Ledger, spokesman acting Maj. Gerald Lewis said, "We're going to try and rectify this and figure out exactly what happened."

THE CRASH

The night was clear and the road was dry as Tanksley drove south on Route 295 at 2:23 a.m. on March 22, 2009. He doesn’t recall any headlights behind him.

Suddenly, he said, there was a screech and another car slammed into the back of his SUV. The rear axle snapped and his vehicle rolled over, coming to rest upside-down on the highway.

"Thank God for my seat belt," Tanksley said. "I was dangling like a puppet."

The crash was so bad the State Police dispatched its fatal accident unit to the scene. The Department of Transportation shut down all three southbound lanes and nearby towns sent emergency services.

Tanksley was concerned for another reason — he had a pistol locked in a box in the back of his SUV, and the crash had thrown it loose. He said he placed the firearm in his glove compartment and told a trooper about it. Tanksley said the .32-caliber pistol was legally purchased in Pennsylvania, where he has a carry permit, but not registered in New Jersey, which has much stricter gun laws. He said the trooper told him not to worry.

Tanksley, cut and bruised, was placed in an ambulance. But suddenly the trooper ran up to him. "He said the other guy is hurt worse than you, get out," Tanksley recalled.

He caught a glimpse of the other driver, who suffered six broken ribs, before the ambulance sped away to Cooper University Hospital in Camden.

At this point, Tanksley had no idea who hit him. And he wasn’t going to learn that from the official crash report. Troopers wrote down the undercover information for Billingham, including a false name, address and company.

Three sources with knowledge of State Police procedures said troopers working undercover are issued fake identification cards but are supposed to use them only to protect an investigation. Once it is clear that an investigation won’t be jeopardized, troopers are supposed to correct the record, they said. (The sources requested anonymity to discuss an ongoing investigation.)

A trooper wrote in the crash report that Billingham "apparently fell asleep," which was echoed word for word by a statement Billingham signed. There’s no description of how fast he was driving.

At the top of the report obtained by the newspaper, a trooper indicated the full document was three pages long. But when Tanksley's insurance company received a copy, it had been modified to say it was only two pages. That copy did not include the diagram of the accident — which correctly identified Gillespie as Billingham. (Both reports were obtained by The Star-Ledger.)

The report was sent to the insurance company not from State Police division headquarters in Ewing but the trooper station in Bellmawr.

"I’ve never seen that happen before," said Jeffrey Pooner, a lawyer who is also representing Tanksley. "It just smells real bad."

PAPER TRAIL

Meanwhile, there was a very different paper trail inside the State Police. Three weeks after the accident, superior officers circulated a memo outlining details of the incident, although alcohol wasn’t mentioned.

The memo, dated April 10, 2009, said Billingham "was at fault in the operation of unmarked troop car 4898" during the accident. It said that he should be "held accountable" and that the accident should be classified as "preventable."

Another memo was addressed to Fuentes, the State Police superintendent, listing both fictional and accurate information for Billingham. Shown the document on Thursday, Fuentes said he did not recognize it, but said he is informed of every crash involving a state trooper. He declined further comment, citing the ongoing internal investigation.

The probe now under way at the Attorney General’s Office started when an anonymous letter alerted investigators, according to two sources with knowledge of the case.

The state sent the investigation into Billingham to the Camden County Prosecutor’s Office in October 2009, according to Jason Laughlin, spokesman for the prosecutor.

To avoid the appearance of a conflict of interest because Billingham’s brother is the Camden County sheriff, the case was transferred to Ocean County about two months later, Laughlin said.

Then it took more than a year for charges to be filed against Billingham. A criminal complaint was filed in municipal court in Lawnside, where the accident occurred, charging him with assault by auto causing serious injury.

Billingham’s lawyer said his client has not been indicted and is entering a not-guilty plea. He declined to comment on any of the other allegations in the case.

Although the criminal complaint said Billingham was under the influence during the crash, the 90-day period in which a drunken driving charge could be filed had expired, under the statute of limitations.

"It took awhile for (the case) to get to us," said Steven Cucci, the assistant prosecutor handling the case. "It bounced around a little bit."

He declined to specify what kind of evidence shows that Billingham was drunk.

The complaint does not identify Billingham as a trooper.

OTHER CHARGES

The day after the accident, Tanksley said he was told to report to the State Police station to pick up his belongings, including his gun.

But when he arrived, he was arrested and charged with weapons possession because he did not have a permit in New Jersey.

"I was like, are you kidding?" Tanksley said. "I get nailed from behind, and now I’m looking at a felony charge?"

Lewis, the State Police spokesman, declined comment on why Tanksley was charged and not Billingham.

The case was assigned to the Camden County Prosecutor’s Office, and Tanksley was allowed into pretrial intervention. He received probation and completed his community service requirement.

The weapons charge derailed Tanksley’s plan to become a Philadelphia police officer. He said he withdrew from the application process when he had to disclose the incident.

"For the first time in my life, I recently was arrested and I am currently on probation," he wrote on a police department form.

"That was my last chance," said Tanksley, who is now too old to apply to the force. "I had to turn down being a cop."

Billingham, although suspended, is still employed by the State Police.