An Arsenal fan died from “profound blood loss” after being stabbed on a Tube platform in west London, a court has heard.
Tashan Daniel, 20, was with his friend Treyone Campbell travelling to The Emirates stadium last September when he was stabbed by Alex Lanning, 22.
Pathologist Ashley Fegan-Earl said Mr Daniel suffered a wound which was 17.5cm (7ins) deep.
Mr Lanning, of Uxbridge, and Jonathan Camille, 20, deny murder.
Jurors were told previously by prosecutor Jonathan Rees QC that the two Arsenal fans were confronted by the defendants after Mr Lanning asked Mr Daniel “what he was looking at” across the tracks at Hillingdon Tube station.
Mr Campbell said “violence erupted” and Mr Lanning and Mr Daniel broke off into a fight on the platform.
As a train pulled into the station, Mr Daniel was stabbed in the heart by Mr Lanning.
Dr Fegan-Earl said that Mr Daniel’s wound was “complex” because of the type of knife used.
The weapon, shown to the jury, was a £200 German-made knife “designed for NATO military aircraft rescues with the capacity to saw through laminated glass and cut through seatbelts”.
“There was a single stab wound to the chest which penetrated the left chest wall, passed through the right atrium of the heart and ended within the right lung,” Dr Fegan-Earl said.
“This led to profound bleeding in the chest and lost two-fifths of his blood.”
Dr Fegan-Earl added that the knife also “partially cut into the breastbone” and that “moderate to severe force” must have been used by Mr Lanning to inflict the injury on Mr Daniel.
The cause of death was blood loss, the pathologist said.
Jurors also heard written statements from passengers who witnessed the boys “scuffling” which “escalated” into the fatal stabbing.
One of them, Angeline Jeganath, was on the Metropolitan Line train from Uxbridge when it pulled into Hillingdon.
She said she recalled seeing four males involved in two separate fights.
“It all happened so fast,” she said, adding that Mr Daniel was trying to defend himself and appeared to be getting the better of Mr Lanning.
“I saw them in an embrace then I heard a woman scream ‘he’s been stabbed’.
“There was blood everywhere – it was just pouring out of him [Mr Daniel].
“There was an intensive care doctor on the train who approached to help. I saw Tashan’s eyes, they were open but not moving.
“His friend was shouting out ‘come on, you’re strong’.”
The trial continues.