Ian Huntley "invented" a defence to fit the facts, the prosecution lawyer at his murder trial has said.
Mr Huntley is into a second day of questioning
Richard Latham QC, cross-examining Mr Huntley, described him as "devious" and a liar who "planned" a defence once he knew of the prosecution case.
Mr Huntley, 29, said he did tell lies but at the time "genuinely believed" he had done nothing wrong.
He denies murdering 10-year-old Holly Wells and Jessica Chapman in August 2002 in Soham, Cambridgeshire.
Mr Huntley admits one charge of conspiring to pervert the course of justice.
His ex-girlfriend Maxine Carr denies helping an offender and conspiring to pervert the course of justice.
Mr Huntley claims Holly accidentally drowned in his bathtub, and that he apparently smothered Jessica while trying to stop her screaming.
He claims the girls were in the bathroom because he had invited them into his house to try to help Holly stop a nosebleed.
Mr Latham called the nosebleed story "rubbish" and said the temptation had been put before him when they arrived on his doorstep.
He said: "Jessica was screaming because you were murdering Holly. That is the truth".
Mr Huntley denied this, but seemed to lose his temper when accused of holding Holly under the water and watching her drown.
After one outburst, Mr Latham asked him if he had lost his temper with the girls, which he denied.
Mr Huntley was questioned by Mr Latham about when he became aware of the prosecution case against him.
He was cross-examined about a conversation he had with his mother in prison on 23 October, which was secretly recorded.
"Some of the things I was apparently seeing... was what I wanted to see.... I can't remember exactly what I said to my mother," Mr Huntley said.
Mr Latham said: "You were working out how to plan your way round the
prosecution case, weren't you?"
Mr Huntley replied: "No, I wasn't."
Reading from Mr Huntley's statement, Mr Latham said: "I'm adamant, I'm 100 per cent
certain I saw those girls leaving the house."
Pausing, Mr Latham then said: "You're a liar, aren't you?"
Mr Huntley said: "That's what I saw. I did tell lies in the two-week period, yes."
Mr Latham dismissed Mr Huntley's assertion that he was "trying to work
out why things were happening towards" him.
"You were being far more devious than that, Mr Huntley, you were inventing a defence to fit the facts."
Mr Latham suggested that Mr Huntley had concocted a story to explain how another person might have gained access to the hangar in the school by saying it was unlocked, in order to explain how the clothes could be found there.
He suggested Mr Huntley had also made up a story that he had rearranged a bin bag in the bin which could explain how his hair was mixed up with the clothes.
He was asked about the conversation with Holly's father Kevin on 7 August, three days after the girls went missing from their Soham, Cambridgeshire homes.
He agreed with Mr Latham's assertions it was inexcusable and had been done to benefit himself, and that he had actively approached Mr Wells rather than being forced to lie.
"I'm well aware of the lies I told," Mr Huntley said about his chat with Mr Wells, when he told him he was sorry.
Mr Latham also asked about his statement in August that he had been the last friendly face the girls would have seen.
Mr Huntley replied: "I was a friendly face."
When asked about remembering the day's events prior to his attempted overdose in prison, Mr Huntley confirmed that he was "changing his approach" to the way he remembered events while at Woodhill prison.
The case continues.