The Beaver County man charged in the shooting death of Dr. Gulam Moonda will plead guilty Monday, rather than stand trial and risk being sentenced to life in prison, sources said yesterday.

Damian Bradford, of Center, will admit his guilt and agree to testify against the doctor's wife, Donna Moonda, saying that they conspired to commit the killing.

Mr. Bradford, 25, and Mrs. Moonda, 47, began an affair after meeting in a drug-rehabilitation center about a year before the crime.

She was under subpoena to appear at Mr. Bradford's trial as a government witness but planned to invoke her Fifth Amendment right to refuse to answer questions.

Mrs. Moonda has professed her innocence. Her lawyer said she was intent on testifying "to set the record straight" until he talked her out of it, fearing what she said would be twisted by prosecutors.

Even after the plea bargain with Mr. Bradford was negotiated yesterday, prosecutors would not discuss it.

Assistant U.S. Attorney Linda Barr would say only that she was still preparing for Mr. Bradford's trial and would be in court Monday.

"If there is a deal, I am not aware of it," she said last evening.

Mr. Bradford's lawyers, Michael DeRiso and Patrick Thomassey, could not be reached.

But sources involved in the case said Mr. Bradford's trial will be called off because he will enter guilty pleas Monday in federal court in Akron, Ohio.

He is accused of following Dr. Moonda, 69, a millionaire urologist from Mercer County, Pa., to the suburbs south of Cleveland, then killing him on the Ohio Turnpike. The formal charges against Mr. Bradford are interstate stalking and use of a firearm in a violent crime.

By pleading guilty and agreeing to cooperate with the government, he hopes to negotiate a prison sentence of less than 20 years.

Bill Edwards, a spokesman for U.S. Attorney Gregory A. White of the Northern District of Ohio, would not discuss Mrs. Moonda or whether a warrant for her arrest had been issued.

The government's evidence against Mr. Bradford was built around science rather than witnesses. He had a half-dozen cell phones, and prosecutors say one marks him as the killer of Dr. Moonda.

The government says cell phone tower tracking technology is so precise it pinpointed Mr. Bradford's movements the day of the killing.

It showed that one of his phones initially was near his home in Beaver County. Then the phone was in the area of Hermitage in Mercer County, where the Moondas lived.

Finally, prosecutors say, Mr. Bradford's cell phone was "near the Ohio Turnpike," where the gunman killed Dr. Moonda with a bullet to the face the evening of May 13, 2005.

In addition to tracking Mr. Bradford's movements, cellular records show that he and Donna Moonda communicated by phone and text message the day of the killing, prosecutors say.

One hurdle the government may have had was that the tracking systems can show only when and where cell phones were used. The technology cannot identify who used them. This means the case against Mr. Bradford would be entirely circumstantial.

But with Mr. Bradford's decision to plead guilty, he corroborates the government's theory of what he did and provides it with something else -- a witness against Donna Moonda.

Long before Mr. Bradford's indictment in March, the possibility of her involvement in her husband's killing hung over the case. U.S. District Judge David Dowd, who will preside at Mr. Bradford's plea hearing, raised that issue last month.

"The widow is a person who may be under some suspicion in this homicide," Judge Dowd said.

Mr. DeRiso, one of Mr. Bradford's lawyers, added a harsher assessment of Mrs. Moonda: "Suspicion is a light word, your honor."

Mr. DeRiso later called her "an unindicted co-conspirator" who was a target of prosecutors.

"It is, and has always been, the government's theory that Donna Moonda conspired with somebody to have her husband killed," Mr. DeRiso wrote in a memo to the judge before his client's plea bargain was struck.

Mrs. Moonda was driving her husband and her mother, Dorothy Smouse, 76, the day of the shooting. She pulled over three times while covering 80 miles of their planned 200-mile trip from Hermitage to Bowling Green, Ohio.

First she stopped so they could eat. She stopped again to buy a bottle of water.

Mrs. Moonda drove about five more miles and stopped a third time in an emergency pull-off on the turnpike. There, she said, her husband was to take over the driving.

He never had a chance. Mrs. Moonda told police a highway robber pulled in behind them and went after her husband.

The thief took Dr. Moonda's wallet, shot him and drove away without harming either of the women.

Mrs. Moonda gave murky statements and told the highway patrol that she could not identify the killer. On May 20, 2005, a week after the killing, an interrogator from the patrol accused her of conspiring with Mr. Bradford.

She stopped cooperating with police that day and soon after hired Cleveland lawyer Niki Z. Schwartz to represent her.

Mr. Schwartz could not be reached yesterday. But he previously said she had nothing to do with her husband's death, and she doubted that Mr. Bradford did, either.

"I would think Donna would be shocked if Bradford had anything to do with this," he said.

In turn, Mr. Bradford portrayed himself as an innocent man for 14 months, much of it spent in jail.

Police raided his apartment after Dr. Moonda's death, looking for evidence that might tie him to the killing. Among the items they seized were six cell phones that would be crucial to the case.

They also found illegal steroids. Mr. Bradford, who calls himself "Kaos," once was interested in bodybuilding and, perhaps, a career in professional wrestling.

He spent six months in jail after pleading no contest to the steroids charge. Six weeks after his release, he was in trouble again, this time on suspicion of assaulting a McKeesport police officer, resisting arrest, disorderly conduct and public drunkenness.

As Mr. Bradford sat in jail in Pittsburgh, a grand jury in Cleveland indicted him in Dr. Moonda's death.

On the one occasion he spoke in court, Mr. Bradford was calm and confident.

"I'm not a bad guy. I have not involved myself in violent crime," he told a Pennsylvania judge last fall. He was seeking parole after his steroids conviction, but seemed to be talking about the Moonda case.

Prosecutors, though, revealed another side of Mr. Bradford when they played tapes of him talking to his girlfriend, Charlene McFrazier. In those conversations, he was loud, profane and cocky. At one point, he told her all the government had on him were cell phone records.

But Ms. McFrazier, 21, of Leetsdale, discovered that those records can be damning.

She lied about being with Mr. Bradford in Beaver County the night Dr. Moonda was killed in Ohio. Ms. McFrazier pleaded guilty to perjury in May, her hand forced by cell phone technology.

Tower tracking showed she was taking calls from Mr. Bradford the day of the killing, so prosecutors said she could not have been with him.

The same science was the best evidence against Mr. Bradford, causing him to change his story and turning him into a witness for the prosecution.