BOSTON -- Mounting debt and dissatisfaction in his sex life drove a British man to kill his wife and baby daughter in 2006, prosecutors told a Middlesex County jury on Friday.

Sex, Money Behind Entwistle Slayings, DA Says | Video: Trial Begins | Special Section: Entwistle Trial

Neil Entwistle, 29, is accused of shooting his wife, Rachel, 27, and 9-month-old daughter, Lillian Rose, on Jan. 20, 2006, in the family's rented home in Hopkinton.

Hopkinton police found the bodies of the young mother and baby under bedding and pillows in the 6 Cub's Path home's master bedroom on Jan. 22, 2006, after her family filed missing persons reports.

"(Police) lifted the foot of the cover at the foot of the bed and they see a foot -- a human foot. They go back around the other side of the bed, they lift the top and they see what turns out to be the face of Rachel Entwistle and Lillian Entwistle," Assistant Middlesex County District Attorney Michael Fabbri said.

Autopsies later concluded that Rachel Entwistle died of a gunshot wound to the head and Lillian died of a gunshot wound to the abdomen.

Using a one-way ticket, Entwistle boarded a British Airlines flight out of Logan Airport the day after the slayings and flew to England, Fabbri said. Police arrested Entwistle in England two weeks later, charging him in the death of his wife and daughter.

"(When he was arrested,) he had a clipping from a local newspaper for escorts and sexual services," Fabbri said.

Two months later, he pleaded not guilty to two counts of murder, illegal possession of a firearm and illegal possession of ammunition in connection with the slayings.

But defense attorney Elliot Weinstein said there is more to the story, and that Entwistle was a loving and devoted husband and father.

"Everyone who knew Rachel and Neil will tell you they loved each other. They were a loving couple," Weinstein said.

Entwistle told police he discovered his wife and daughter dead after doing errands on Jan. 20, 2006. He said he covered their bodies, considered suicide and left for England to be consoled by his parents without calling police or Rachel Entwistle's parents.

Weinstein said his client's actions after the slayings were consistent with those of a grief-stricken man.

"Everything he said and everything he did thereafter, he did because he loved them, he did because he loved them both," Weinstein said.

But in his opening statements, Fabbri painted a picture of a man with a dark side who was deep in debt and unhappy with his sex life. He said in the months before the killings, Entwistle visited Web sites of escort services and e-mailed women to discuss setting up discreet relationships. He also visited more macabre Web sites, Fabbri said.

"In the days just before Jan. 20, 2006, the defendant visited Web sites about killing and suicide," he said.

Entwistle, a computer engineer, was unemployed and faced mounting debt, including the $2,700 a month rent for the home they moved into on Jan. 10, 2006.

Weinstein countered that the couple was computer savvy and other people also had access to their computer.

But a key piece of evidence for the prosecution is the gun used to kill the woman and baby. Fabbri said Entwistle's DNA was found on the .22-caliber Colt revolver, and Rachel Entwistle's DNA was found in and on the muzzle of the gun.

"The DNA of Rachel Entwistle -- who had no interest in firearms, who had never touched those firearms -- was on that .22-caliber Colt," Fabbri said.

The gun used in the slayings is owned by Rachel Entwistle's stepfather, Joseph Matterazzo. The prosecution said Neil Entwistle stole the gun from his in-laws' Carver, Mass., home and returned it after the shootings.

Weinstein urged the jury to look beyond stereotypes.

"The evidence that you are going to hear is going to be sordid. It is going to be gruesome and it is going to be graphic. Neil Entwistle is not guilty," Weinstein said.

The first witness, Rachel Entwistle's mother, Priscilla Matterazzo, said that her daughter and son-in-law appeared to have a loving relationship. She said, to her knowledge, there was no history of violence in the relationship and she considered Neil Entwistle to be a loving, trusting and devoted. But she also said that she did not see her son-in-law at the services for her daughter and granddaughter.

The case sent shockwave across the world and set off an international media frenzy. Weinstein argued unsuccessfully for a change of venue, saying his client would not be able to get a fair trial.

After four days, a 12-person jury and four alternates were selected from an original pool of 170 people.

Entwistle's parents, Cliff and Yvonne, sat behind their son in the Middlesex County courtroom as the proceedings got under way on Friday. Rachel Entwistle's stepfather and about a dozen other friends and relatives were also present.

The witness list is very long, and the trial could run until the first week in July.

The Entwistles married in 2003 after meeting four years prior at Britain's University of York, where Rachel Entwistle was studying abroad through the College of the Holy Cross. They lived in England for two years before moving back to Massachusetts in 2005.