The father of a boy whose throat was slashed when he was attacked along with a friend collapsed as his son's injuries were read out, a court heard.
Steven Bayliss and Nuttawut Meechao died in 2005
Steven Bayliss, 16, and Nuttawut Meechao, 14, were killed with a hunting knife in Finchampstead, Berks, in 2005.
David Bayliss was taken from court after a forensic expert said his son died "almost instantly" from the wound.
Thomas Palmer, 19, of Blagrove Drive, Wokingham, pleaded not guilty to two murder charges at Reading Crown Court.
Forensic pathologist, Dr Ashley Fegan-Earl, told a court on Tuesday it was likely that the wound was caused by an assailant standing behind the teenager.
Steven was stabbed several times more "suffering four injuries that could have killed him as well as three superficial wounds", a court heard.
But Dr Fegan-Earl said the throat injury "would have led to a very rapid collapse and death", adding Steven's other wounds had not bled as they would if he had been still alive when they were inflicted.
At the start of the trial on Monday, prosecutor Julian Boughon had said it was a "straightforward case of murder".
Earlier the court had heard that the teenagers were socialising and drinking alcohol ahead of their first day at college the following morning.
But Steven, Nuttawut Meechao - known as T.Wood Nadauld - and Mr Palmer became separated.
The court had heard Steven was attacked with "such ferocity that police who found his body believed that an attempt had been made to sever his head from his shoulders".
A six-and-a-half inch (17 centimetre long) blade was used to stab the two boys.
Nuttawut, who had moved from Thailand a few years before, was stabbed in the chest and received more than 20 other wounds, a court heard earlier.
Police were alerted when Mr Palmer made a call saying that "somebody has been cut a little".
In a police interview, heard in evidence on Tuesday, Mr Palmer maintained that the boys disagreed and a fight ensued.
He said: "I couldn't think straight at the time because we had been drinking."
But the court was told by a medical expert that there were no drugs or alcohol found in Mr Palmer's bloodstream, indicating that he could not have been intoxicated.
The trial continues.