Ross Parker, 17, of Bozeat Way in Peterborough, was walking home with his girlfriend when he was allegedly attacked and fatally stabbed by a gang in September 2001.
Shaied Nazir, of Cromwell Road in Peterborough, told Northampton Crown Court the four were just out celebrating his recent marriage.
Mr Nazir, 21, Ziaraff Mahrad, 21, Ahmed Ali Awan, 22, and Sarfraz Ali, 25, all deny murder.
Baseball bat
Mr Nazir, the first of the four to give evidence, told the court racial tensions had been high in the area due to the 11 September attacks 10 days previously.
Gangs of white youths had been roaming the streets, he said, and his family kept a baseball bat by the front door in case of trouble.
Asked by his barrister Michael Lawson QC, whether he had contemplated beating anyone up, or worse, Nazir replied: "No".
He admitted that when arrested the day after the attack, he had at first told police he had not been at the scene.
"I was an idiot for lying," he said.
Earlier the court had heard the gang sprayed an aerosol in Mr Parker's eyes before they punched, kicked, and hit the teenager with a panel-beater's hammer.
Prosecutor Stephen Coward QC, said the four then stabbed him with a foot-long hunting knife.
The hearing was adjourned until Thursday.