The attack happened on Waverley Bridge.
Stabbed Pupil Bailey Gwynne Had "No Chance"
A teenager stabbed during a fight at a school had "no chance'', a court has been told.
Bailey Gwynne, 16, died from a single knife wound after a fight at Cults Academy in Aberdeen on October 28 last year.
A 16-year-old youth denies murder and is on trial at the city's High Court for a fifth day.
In his closing speech to the jury, prosecutor Alex Prentice QC urged them to "do justice'' in the case and return a verdict of guilty to the charge of murder.
But defence QC Ian Duguid said the case centred around an incident which happened "in the blink of an eye'' within 30 seconds.
Mr Prentice began by asking the jury to consider one question.
"Why do you think a young man would carry a knife and a knuckleduster?'' he said.
He went on: "You would have to have hearts of stone not to be moved by the emotion of this trial but you must put emotion aside.''
He said that murder can be committed where a person displays such "wicked recklessness'' that they do not care whether someone lives or dies.
"In this case, there was a stab wound to the heart inflicted by a lethal weapon which was routinely carried by (the youth),'' Mr Prentice said.
"I suggest this case demonstrates so aptly the dangers inherent in carrying a knife.''
The prosecutor said it was not a case of self-defence and asked the jury to consider four things - that the accused ``carried a knife and a knuckleduster'', that he knew the dangers of carrying a knife, that the folding knife was open when it was used, and that ``the knife was directed at the chest and driven home''.
He told the jury: ``Bailey Gwynne had no chance.''
Concluding, Mr Prentice told the 15 men and women of the jury: "If it were only so that we could all turn time back and reverse that morning.
"But your task as judges is to act dispassionately and with obedience to your oath and to return a true verdict according to the evidence, to do justice to this case.
"In my respectful submission to you, to do justice is to return a verdict of guilty to the charge of murder.''
The jury also heard it was open to them to convict the accused of the lesser charge of culpable homicide.
Mr Duguid told them the case centred around a 30-second period in which the incident took place and warned them not to be "blinded'' by prejudice about individuals who carry knives.
He argued the accused had shown ``extraordinary stupidity'' in having a weapon on him but that Bailey had shown "recklessness'' in assaulting the youth.
The QC also maintained the Crown case misses out the evidence of four eye-witnesses as to what happened that day.
He described Bailey as the "aggressor'' during the incident and said there was nothing to suggest the accused chose the spot on the chest to drive the weapon home.
"This, you might think just a chance encounter on a day when nobody was expecting anything to happen and it built up and he was dead within perhaps two minutes of that incident, which had taken no longer than 30 seconds from start to finish,'' Mr Duguid said.
Police are investigating the attack.
Opposition parties are criticising the figures.
The tragedy happened near the village of Benderloch outside Oban on Sunday.
Most Viewed Pictures On Heart
Recently Played Tracks
To listen live, choose your preferred station:
Now playing: The best feel good music
Deposit £10 to get a £40 Welcome Bonus - That's £50 to play bingo, slots and more!*
Over 50 tracks to make you feel-good. New album out now...
Find your local four day weather report here.
Make Heart the soundtrack to your day and you could be a winner with great prizes up for grabs throughout the day.
Find out more about some of the companies advertising on Heart Scotland- East.