Kasey Gordon PIC: Metropolitan Police/PA Wire

A knifeman will be sentenced today for killing a schoolboy and attacking pupils in a “scene of carnage” near their school.

Kasey Gordon, 15, died after being stabbed in the heart in the 30-second onslaught which left three other boys injured.

Serif Aslan, a mentally ill Turkish man, was found guilty last month at the Old Bailey of murder and wounding.

The 34-year-old lived in care in the community hostel near Kasey’s school in Tottenham, north London.

He had been warned against carrying a knife and his tendency to stare at young women.

In January last year, Aslan was punched by a schoolboy after he made a remark to the boy’s girlfriend.

Aslan, who suffers from paranoid schizophrenia, went up the road and returned after buying a £1.49 kitchen knife which he hid in his hand with tissue paper.

He stabbed the 16-year-old boyfriend and other boys who tried to help him.

Witnesses said Aslan calmly walked away after the attack in West Green Road, leaving Kasey bleeding to death on the pavement.

Richard Horwell QC, prosecuting, said: “This main part of the incident lasted about 30 seconds and, when it was over, the defendant calmly walked away.

“He left behind a scene of considerable carnage. The knife that he had carried - the knife he had been told not to carry - was used by him to devastating effect.”

Aslan, of Phillip Lane, was found guilty of murder, two counts of wounding with intent to cause grievous bodily harm to boys aged 14 and 16, and causing actual bodily harm to a 14-year-old boy.

The 16-year-old boyfriend, who like other surviving pupils cannot be identified, was stabbed in the chest but survived.

He told police in a video interview that Aslan told him: “Your girlfriend is very beautiful.”

“I told him to move on,” said the youth. “He pushed me and said, ‘I will f*** you up’.

“I knew he had problems. He is always round my school. He is always looking at the girls, always making comments.

“He pushed me three times and we started fighting. I hit him in the face and he backed off. Then he came after me. He tried to attack me and I tried to defend myself.”

The 14-year-old victim was stabbed near his right hip bone and the second 14-year-old was treated for superficial cuts to the right side of his face.

A few months before the attack, Aslan had been caught with a knife in his room. Police were called and warned him against carrying a knife in a public place.