The jury trying Briton Neil Entwistle over the murders of his American wife and baby retired to consider its verdicts today.
Judge Diane Kottmyer told the jurors to put aside any emotions and to come to their verdicts, which must be unanimous, based upon reason and judgment.
Entwistle denies killing his 27-year-old wife Rachel and their nine-month-old baby Lillian Rose on the four-poster bed in their new home in Hopkinton, Massachusetts, on January 20 2006.
The jury will have to decide whether Entwistle is guilty of first degree murder, if he acted with deliberate premeditation and malice; guilty of second degree murder, if he intended to cause death or grievous bodily harm; or not guilty.
Entwistle, wearing a dark suit and tie, entered the court smiling and sat next to his lawyers at the back of the court, directly in front of his parents Yvonne and Cliff, and younger brother Russell, all from Kilton, Worksop.
Across the aisle in the front row of the public gallery, Rachel's mother Priscilla and step-father Joseph Matterazzo sat with around a dozen of her friends and relatives.
The court has heard from 46 witnesses and the jury was sent out at 9.10am local time (2.10pm BST) on the 13th day of the trial.
"You must spend whatever time is necessary to reach a fair and just verdict," the judge told the jurors yesterday.
Former IT worker Entwistle, 29, from Kilton, Worksop, faces life in prison without the possibility of parole if convicted of the double murders.
He had a secret life in which he trawled the internet for escorts and looked at websites about bankruptcy, killing and suicide before shooting dead his family, US prosecutors said.
In the days before the murders, he trawled sex websites looking for "a bit more fun in the bedroom" and searched the internet for "how to kill with a knife".
He was jobless, his eBay scams and internet businesses were failing, and he had no means of supporting his young, happy family.
Along with mounting debts, he had also just paid more than £4,000 up-front for a three-month lease on the four-bedroom Colonial-style house in Hopkinton, which he moved into less than ten days before the murders.
But Elliot Weinstein, defending Entwistle, suggested Mrs Entwistle killed baby Lillian before committing suicide and that Entwistle was simply a loving husband trying to "protect her honour" and cover it up by moving the gun away from where their bodies were found.
The court heard a post-mortem examination found Mrs Entwistle was shot in the forehead at close range and Lillian was killed with a bullet which passed through her abdomen and lodged above her mother's left breast as she cradled her on the bed.
Assistant district attorney Michael Fabbri, prosecuting, urged the jury to use their common sense and dismiss the suicide theory.
Pointing to Entwistle, he went on: "There is one person responsible for these murders and that person is sitting right over there. He's the one who pulled that trigger twice.
"Neil Entwistle and no one else is responsible for these murders."
During his closing speech, in which he waved the .22 calibre Colt revolver with its long black muzzle around the courtroom, Mr Fabbri accused the defendant's lawyers of highlighting "red herrings" and added: "This was a homicide, not a suicide."
Holding the gun above his head with both hands, he went on: "It could not have happened the way they said it happened."
Entwistle's DNA was found on the grip of the .22 Colt revolver used to kill his wife and daughter, an ammunition container and a gun lock, while the DNA of Mrs Entwistle, who had no interest in guns, was found "both in and on the muzzle" but not on the grip, the court heard.
But Mr Weinstein told the jury his client returned home from a shopping trip to find the bodies in the master bedroom.
"First, Rachel put Lillian over where she thought her heart was and shot her," Mr Weinstein said.
"The bullet travelled through Lillian and into Rachel's left breast."
Holding his hands together above his head, Mr Weinstein went on: "Then she pointed the gun towards her head, steadied it with both hands and fired. She struck herself in the forehead. Death was instantaneous."
Addressing the jurors directly, Mr Weinstein told them: "No one benefits if you allow the nightmare to continue by convicting Neil of something he did not do, could not do.
"The time has come to find Neil Entwistle not guilty."
Earlier, he said things "aren't always what they first appear to be" and that investigators had "Neil did it" filters after noting his name as a suspect on their field work even before visiting the scene.
"The investigation filters, the 'Neil did it' filters, prevented a clear picture from emerging," he said.
He dismissed the evidence that Entwistle used the sex and swinger website Adult Friend Finder and websites such as HalfPriceEscorts.com and hotlocalescorts.com as irrelevant, and went on to dismiss the Entwistles' financial problems as "a few debts from college".
The lawyer, who wears cowboy boots in court, also suggested that Mrs Entwistle's mental status may have been in question and accused the prosecution of failing to provide all the evidence.
"You have the right to expect more," he told the jurors.