RALEIGH — A key piece of evidence that helped convict a Cary man of first-degree murder was uncovered by police within weeks of his wife’s disappearance, prosecutors said today.

Cary police investigators discovered a map on Bradley Cooper’s computer in August 2008 showing the site where Nancy Cooper’s body was found, Assistant District Attorney Boz Zellinger said. The map bore the date stamp of July 11, 2008, one day before Nancy Cooper disappeared, Zellinger said.

“The investigation was called inept and dishonest by the defense, but law enforcement officers in Cary went to great lengths to preserve and analyze all the evidence,” Zellinger said.

The jury returned the verdict against Cooper, 37, shortly before 4 p.m. today after deliberating over three days. Cooper showed little emotion as the judge read the verdict in a Wake County courtroom and he was sentenced to life in prison without parole. The prosecution had not sought the death penalty.

Cooper said his wife went out for a jog at 7 a.m. July 12, 2008 in their Lochmere neighborhood and never returned.

His attorneys argued that Cary police botched the case by zeroing in on their client from the start, failing to investigate leads to other potential suspects.

“We are disappointed at the jury’s verdict, and believed the case for Brad’s innocence was strong,” defense attorneys Howard Kurtz and Robert Trenkle said in a statement. “It is our belief that the appellate issues are strong and we hope to have another chance to exonerate our client in the future.”

Superior Court Judge Paul Gessner ruled immediately after the verdict that there would be no bond for Cooper during the appeals process.

The defense attorneys criticized Gessner’s decision to disqualify certain witnesses.

“We feel that, had the jury been permitted to hear the testimony of our computer experts, the verdict likely would have been different,” the attorneys said.

Cary Police Chief Pat Bazemore said Cooper’s conviction “brings a terrible chapter in our community to a close.”

In a news release, Bazemore thanked investigators who worked on the case, saying they were “accurate, thorough and complete” in their work.

Assistant District Attorney Howard Cummings said he was somewhat disappointed that Bazemore did not appear in court at all during the trial.

Over the course of the eight-week trial, prosecutors presented evidence that Cooper strangled his wife sometime between late on July 11, 2008, after Nancy Cooper left a party at her neighbor’s home, and the following morning, when a friend reported her missing.

Witnesses testified the couple, whom they said appeared headed for divorce, argued at the party.

Nancy Cooper’s body, clad only in a jogging bra, was found at a construction site in a subdivision less than three miles from the couple’s home on July 14, 2008. Prosecutors called witnesses who said Cooper had shown a seemingly nonchalant attitude during the two-day search for his missing wife.

Cooper had been jailed since October 2008, when Cary police arrested him in his wife’s death. Jurors also could have convicted him of second-degree murder.

“Our relief is pretty palpable,” said Garry Rentz, Nancy Cooper’s father. Both her parents and her twin sister, Krista Lister, and brother, Jeff Rentz, were in the courtroom when the verdict was read by Gessner, who cautioned the audience against expressing emotion.

The victim’s family and friends hugged and smiled through tears when the first-degree murder verdict was announced. Gessner polled the jurors individually and urged them not to second-guess their decision, even though the widely publicized case would be talked about, written about and become “the subject of a television documentary and possibly even books.”

The case has received media attention in the U.S. and Canada, where both Nancy and Bradley Cooper were born and raised. The Coopers were newlyweds when they moved to Cary from Edmonton, Alberta, in 2001 for Brad’s job at a high-tech firm in Research Triangle Park.

The couple had two daughters while living in North Carolina. Seven-year-old Bella and 4-year-old Katie Cooper have been living in Canada with their mother’s family since shortly after Nancy Cooper’s body was found.

“We’re going to go home and get our lives back,” said Garry Rentz after the verdict, echoing a complaint the judge heard from jurors as the trial ran on.

In closing arguments Tuesday, defense attorneys hammered repeatedly on what they called a lack of hard evidence linking the defendant to his wife’s death.

“No blood, no bodily fluids, no fibers,” attorney Robert Trenkle said.

Prosecutor Cummings said the reason for the lack of that evidence was that Brad Cooper had cleaned the home so thoroughly. But there was other evidence, he said.

“The day before your wife is missing, you Google where the body is dumped?” he said. “You would have to know something is wrong.”

Much of the testimony in the case was highly technical, based on police analysis of cell phone towers, video monitors and computer hard drives.

The prosecution even presented evidence that the defendant, a Cisco-certified voice-over-internet specialist, might have arranged a fake phone call to his cell phone to try to prove Nancy Cooper was still alive when prosecutors contend she was dead.

“There was a lot of technology in this case, but it still followed a pretty universal theme,” Zellinger said.

Jurors heard a friend of Nancy Cooper’s testify that the couple’s marriage began to deteriorate after he told his wife in late 2007 that he’d had an affair with one of their good friends, and that they were constantly at odds. Another friend of the victim’s said she was so concerned about Nancy Cooper’s well-being that she contacted a domestic-violence program for advice in February 2008. The friend said Bradley Cooper had taken control of the family finances and made written plans to close the couple’s bank and insurance accounts.

Nancy Cooper’s parents pledged today to continue supporting efforts to educate people about domestic violence. Nancy’s Butterfly Fund, a foundation started by family and friends of Nancy Cooper, assists victims of domestic abuse.

“Domestic violence has to stop,” said Nancy’s mother, Donna Rentz.

Krista Lister, who has custody of Bella and Katie, said today that the girls are doing well.

“They want me home for Mother’s Day,” she said. “They’re awesome girls.”