A teenager who killed a US tourist and stabbed five others during a frenzied knife rampage in Russell Square has been given an unlimited hospital order.

Zakaria Bulhan murdered Darlene Horton, 64, with a large kitchen knife which he used to attack five other strangers in short succession.

The 19-year-old was seen skipping and with a "crazed smile" as he lunged at passers-by in the central London tourist hotspot around 10.30pm on August 3 last year.

The attack initially sparked fears it was terror-related because it was near a 7/7 memorial, and came at a time of heightened tensions due to attacks in Paris and Brussels in the preceding months.

But Bulhan, who was born in Norway to Somalian parents, was found to have been suffering from paranoid schizophrenia at the time of the attack.

He said he heard voices during the attack, that the devil had made him kill and he was being tracked by the secret service.

Bulhan admitted manslaughter by diminished responsibility, and five counts of wounding with intent to do GBH, which were all accepted by the Crown.

At the Old Bailey today, he was given a hospital order, with an indefinite restriction order.

Sentencing him, Mr Justice Spencer said: "Armed with a large kitchen knife, in the space of just a few minutes you attacked and stabbed these six victims indiscriminately and at random.

"Tragically Darlene Horton died at the scene.

"One of the others sustained particularly serious injuries, with long term consequences.

"All were profoundly affected by this dreadful experience.

"These were crimes which caused enormous public concern because, from their timing, it was feared it might be the work of a terrorist fanatic.

"As it turned out they were not, although that is no consolation to your victims."

He added: "It was a tragic waste of life.

"Ironically, as a special needs teacher Darlene Horton had devoted her working life to young people with disabilities and mental illness.

"London was one of her favourite places. Words cannot convey the family's sense of loss and bewilderment that such a thing could happen.

"It was quite clear that when you committed these dreadful crimes, you were not in your right mind. You were in the grip of a psychotic illness - paranoid schizophrenia.

"I do not overlook the worrying feature that somehow, and somewhere, you acquired this large kitchen knife and armed yourself with it.

"You said you could not remember why you had the knife, although you did remember throwing away your phone and some of your clothes because you believed that the secret service were tracking you."

The judge added: "You took the life of an innocent member of the public. Her husband and her daughters will never come to terms with that loss.

"You stabbed five other people that night. Two of them in particular have been very badly affected by what you did to them.

"I accept that you are deeply sorry for what you did and at the time you were very unwell mentally.

"You will remain at Broadmoor Hospital in conditions of maximum security probably for a very long time indeed."

Bulhan showed no emotion as he left the dock.

In the months leading up to the attack, Bulhan began acting oddly, and was referred to his local community mental health trust in East Wandsworth in April.

But he was deemed to be suffering from low moods and anxiety, and referred to his GP.

On the day of the attack, his father had taken him to a mosque in Whitechapel, east London, to see an imam for help.

But Bulhan fled after he became convinced worshippers were trying to blow "magic spirits" in him.

He was next seen outside a restaurant further up the road at about 6pm, but was not spotted again until he entered Russell Square at about 10.20pm.

After the rampage, Bulhan was tasered and arrested at the scene, and heard by police repeatedly muttering "Allah".

In his tracksuit bottoms he was carrying a small pamphlet called "Fortress of the Muslim" - but prosecutors said this carried no relevance.

Retired teacher and mother-of-two Ms Horton was due to return to the US the next day with her childhood sweetheart and husband, Professor Richard Wagner.

The couple spent their last evening at a restaurant in Bloomsbury, and were walking back to their hotel when they were caught up in the horror.

Ms Horton was stabbed in the back, and died at the scene.

The five other victims - US citizen Martin Hoenisch, 59, Lillie Sellentin, 23, an Australian tourist, David Imber, 40, also on holiday from Australia, Bernard Hepplewhite, 65, who had travelled the West End from his London home to see a show, and Israeli tourist Yovel Lewkowski, 18 - recovered from the events.

In a statement Professor Warner said: "We suffered an unspeakable tragedy because of potential unknowable deficiencies in our system of identifying and treating individuals with mental illness, in his family and life circumstances, and in our knowledge about mental illness.

"As a result a potential killer was allowed to walk the streets."