Neil Entwistle wrote about selling his story to "the highest bidder" after he shot and killed his wife and baby daughter, a court heard today.
Assistant District Attorney Michael Fabbri, prosecuting, told the jury at the Middlesex County Superior Court in Woburn, Massachusetts, that the 29-year-old former IT worker trawled the internet for escorts and websites about killing and suicide.
Entwistle denies shooting dead his 27-year-old American wife Rachel and their nine-month-old daughter Lillian Rose at their home in Hopkinton, Massachusetts, on January 20 2006.
Mr Fabbri said Entwistle was arrested in London on February 9 with a notebook in which he had written "how he wants to sell his story to the highest bidder".
On the other side he had written how he loved his wife and daughter, Mr Fabbri said.
He said the couple had a "loving, nourishing and stable" relationship with his family, but added: "There is another side to Neil Entwistle".
The prosecutor told the jury of eight men and eight women that Entwistle told police: "After I came and found them in the bed I covered them up.
"It was like I was closing them off.
"My first thought was to go downstairs and get a knife from the kitchen to hurt myself, but I knew that would hurt so then I decided to get in my car and leave the Hopkinton home".
He said Entwistle told police he wanted to "kill myself".
Mr Fabbri added that between late December 2005 and mid January 2006 Entwistle went to the Adult Friend Finder website "a number of times and began exchanging emails with females and discussing the possibility of setting up discrete relationships".
He also searched the internet for information about bankruptcy, "killing and suicide".
Mr Fabbri said: "There's only one true verdict in this case and one murderer in this case, and that's the defendant."
He said the last time anyone but Entwistle saw his wife Rachel was on 19 January, 2006, and in the following days her family and friends became concerned.
He described the scene when two officers searched the house a second time after noticing a smell on 21 January, 2006.
As they entered the master bedroom they went to the far side of the bed and saw a human foot as they lifted the blanket.
Moving to the top of the bed, they lifted the blanked and "see what turns out to be the face of Rachel and Lilly Entwistle".
The prosecutor also told the jury that Entwistle called Rachel's stepfather Joseph Matterazzo and said: "I don't know how it got this way. I was only gone for a couple of hours. Someone shot them."
He claimed he had gone to Staples to buy some computer equipment at about 9am on 20 January, and returned about two hours later.
When he returned to the home on Cubs Path in Hopkinton, Massachusetts, he said he found the bodies and said: "She looked asleep."
"He pulled the covers back a bit and claimed he could see bubbles on Lilly and a hole on Lilly."
But Mr Fabbri said it took hours for crime scene investigators to discover the causes of the deaths.
On 9 February, when Entwistle was arrested at the Royal Oak underground station in London, he was with his friend Dash Munding who told him the police were on their way and suggested they meet them.
"The defendant says something to the effect, 'Is there another way out of this platform?"' Mr Fabbri said.
When he was arrested, Entwistle also had a local newspaper clipping about "escorts and sexual services".
In the public gallery, Entwistle's mother Yvonne, of Kilton, Worksop, held a tissue to her face as the opening statements were delivered.
She has said the family believe her son is "100 per cent innocent" and sat directly behind him with her husband Cliff, a Bassetlaw district councillor, and her other son Russell.
Later, Elliot Weinstein, defending Entwistle, told the jury: "The evidence you are going to hear is going to be sordid, it's going to be graphic and it's going to be gruesome.
"Do not be overwhelmed.
"The evidence will show you that Neil is not responsible for killing Rachel or killing Lillian. Neil Entwistle is not guilty."
He went on: "On 20 January, 2006, Neil Entwistle's world changed, never to be the same.
"Neil's life changed, also never to be the same.
"Neil loved his wife and Neil loved his daughter.
"On 20 January he lost them both.
"Everything that he said and everything that he did thereafter he did because he loved them, he did because he loved them both."
Mr Weinstein said the prosecution had set out their case, but warned the jury: "If it was that clear and if it was that easy, we wouldn't be here. But it's not that clear and it's not that easy.
"There's nothing typical about the evidence you're going to hear."
Rachel's American mother Priscilla, stepfather Joseph Matterazzo, and brother Jerome Souza were among around a dozen members of Rachel's family at the courthouse today.
Her parents have accused their son-in-law of an "unbearable" betrayal.
Earlier this week, as the jury was selected from 189 members of the public, Entwistle's defence team called for the trial to be dismissed after a potential juror said she overheard other jurors saying: "Fry him, send him away."
Mr Weinstein told the judge that the disclosure showed Entwistle could not get a fair trial and called for the proceedings to be dismissed because the jury pool had been "infected".
But Judge Diane Kottmyer said the jurors who had been selected had shown they were fair and impartial and denied the motion.
Entwistle denies two counts of first degree murder, possession of a firearm and possession of ammunition.
Prosecutors believe he shot and killed his wife and daughter in the house they were renting in Hopkinton before fleeing the US for his parents' home in Worksop the following morning.
He ran up debts before the murders, his internet businesses had failed and he had no visible means of support.
Mr Weinstein has said his client could not get a fair trial in the US because of the media interest in the case.
Entwistle faces life in prison without the possibility of parole if convicted of the double murder.