During a cross-examination in which his mother fainted, James Petrolini admitted he opened his birthday cards on the bus home to Oxford a few hours after slashing the throat of Mohammed el-Sayed while Richard Elsey, a fellow student, allegedly held the victim.
He said Elsey, 19, who is also accused of murder, fell asleep on the return journey.
Petrolini, who kissed then raised his rosary beads towards his parents when he entered the dock, complained of feeling ill after his mother collapsed.
The court was adjourned for a over an hour.
The jury heard that while he was in prison, Petrolini, a former Gordonstoun schoolboy, told a psychiatrist he 'was on a high, completely relaxed, empty and with no confusion' after killing Mr el-Sayed, 44, a father of two.
The psychiatrist reported that Petrolini said he had 'quite enjoyed' the killing at the time and had continued to stab his victim until he stopped breathing. Yesterday Petrolini denied saying he had enjoyed the attack.
Petrolini claimed that he had been visited by his parish priest in prison and asked if Elsey's 'eyes were his own'. The priest had said that if they were not then Elsey was possessed by the Devil.
'He (the priest) said that if you are possessed by the Devil you invited him in,' Petrolini said. 'I remembered all the poems Mr Elsey wrote about being in league with Lucifer.'
A prison report stated Petrolini spoke of his offence and situation in an 'unrealistic' manner. While he accepted that he would no longer be able to join the Royal Marines, he did not see any problem in becoming a lawyer. He had written to the Law Society seeking advice.
Petrolini denied trying to blame Elsey for a murder he had committed and that he had been alone when he killed Mr el-Sayed. He said Elsey had 'revelled' in the killing.
Perolini also denied threatening to rape Elsey's girlfriend to prevent him going to police.
He said he had been 'spaced out' and under Elsey's control when he killed.
'Why would I want to kill someone on my birthday?' he asked Conrad Seagroatt QC, Elsey's counsel.
The prosecution claims that Petrolini and Elsey, who were repeating their A-levels at a private Oxford crammer, shared an obsession with the SAS and that killing Mr el-Sayed was their 'ultimate dare'. They are alleged to have chosen Mr el-Sayed at random and jumped into his car when it stopped at a junction in Bayswater, west London, on 14 January.
Petrolini, of Grantown-on-Spey, Highland, and Elsey, of Beaconsfield, Buckinghamshire, both deny murder. Petrolini has admitted manslaughter on the grounds of diminished responsibility. He claims he believed Elsey was an SAS officer and that the killing was an initiation test.
Elsey claims he was not in Mr el-Sayed's car when the killing took place and that he believed Petrolini only intended to rob the man.
The trial continues today.Reuse content