A teenager today admitted killing an American tourist and stabbing five others during a knife rampage.

Zakaria Bulhan, 19, fatally stabbed Darlene Horton, 64, before attacking five other people - including Medway man Bernard Hepplewhite - with a kitchen knife in Russell Square, central London at about 10.30pm on August 3.

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

But Bulhan was found to have been suffering from paranoid schizophrenia at the time of the attack, although he was ruled fit to plead last December.

Bulhan, a Norwegian national of Somali descent, appeared at the Old Bailey today in the dock flanked by medical and security staff.

He stood emotionless as he pleaded not guilty to the murder of Mrs Horton but admitted manslaughter on the grounds of diminished responsibility.

Bulhan, of Tooting, south London, denied five counts of attempted murder, but pleaded guilty to five counts of wounding with intent to do GBH.

All his pleas were accepted by the Crown due to his mental health issues and the counts of attempted murder were ordered to be left to lie on file.

At the time of the attack, retired special needs teacher Mrs Horton was due to fly home the next day.

She was stabbed in the back with a kitchen knife and died in the street in front of her husband Richard Wagner, a Professor of Psychology at Florida State University.

Bulhan then knifed five other people in the street on the same day - Mr Hepplewhite, Martin Hoenisch, Lillie Sellentin, David Imber and Yovel Lewkowski before police arrived and tasered him.

Mr Hepplewhite, 67, from Wainscott near Rochester, was knifed in the stomach in the brutal attack.

Despite his injuries, he took the time to email colleagues at the Historic Dockyard in Chatham from hospital to apologise because he wouldn't be able to turn up

.

At today's hearing, Mark Heywood QC, prosecuting, said: "The defendant was suffering from an acute episode of mental illness, which has been diagnosed as paranoid schizophrenia.

"The test for the alternative charge under the heading diminished responsibility is easily satisfied.

"This was a wide scale concerted attack on a number of individuals using a large knife, often directed, albeit by single blows, to the abdomen and upper chest" - Mark Heywood QC, prosecuting

"Substantial impairment, that being common ground between the parties based on considerable expertise and experience of the doctors.

"The Crown has come to the view that it is proper in this case to accept the plea."

He added: "This was a wide scale concerted attack on a number of individuals using a large knife, often directed, albeit by single blows, to the abdomen and upper chest.

"Those who have interviewed him for the purpose of the medical examination found that he has said on occasion he cannot recall the events that have happened.

"It is difficult to elicit a complete account.

"Having regard for the pleas now tendered, the Crown has reached the view it is proper to accept."

The prosecutor said: "Of the six stabbed by the defendant in that short period of activity, five suffered non-fatal injuries and have since made, for the most part, good and relatively swift recoveries.

"However one, Darlene Horton, an American citizen who was that day a visitor to the United Kingdom at the time, received a stab wound to the back which penetrated her left lung and her heart, a devastating injury from which she died at the scene."

The court heard Mr Hepplewhite, the first victim, described seeing the man "bustling" towards him, as if he was impatient.

Mr Haywood said: "Without saying anything, he approached and he seemed to punch Mr Hepplewhite. There was some force in it, rather more than play fighting.

"The man, to him, showed no signs of anger, he simply skipped straight on, swaying his arms."

Bulhan then attacked Miss Sellentin, who also thought she had been punched, before he carried on along the street.

She approached Mr Hepplewhite and asked if he too had been punched.

Someone shouted "he's got a knife" - at which point they both realised they had been stabbed.

Bulhan then attacked Ms Horton, and her husband Mr Wagner heard her say "ouch".

But her reaction gave no clue about how serious the attack was, so Mr Wagner started to briefly chase after Bulhan.

Another witness described Bulhan inserting the knife into Ms Horton's back "up to the hilt", the court heard.

Bulhan went on to attack three more people, including Mr Imber, who made brief eye contact with him.

Mr Heywood said: "He described the man as having what he called a 'crazed smile', either as if he was enjoying it or that he was under the influence of drugs."

Bulhan eventually headed into Bedford Place, where he was arrested and taken to hospital for a head injury from falling to the ground as he was tasered.

Mrs Horton was in London with her husband as he taught in the summer session at Florida State University's renowned London Study Programme.

The organisers of the overseas study programme expressed their deep sadness at the tragic loss.

FSU President John Thrasher said: "There are no words to express our heartache over this terrible tragedy.
"We are shocked that such senseless violence has touched our own FSU family, and we will do all we can to assist Professor Wagner and his loved ones, as well as his friends and colleagues in the psychology department, as they mourn."

Rick Scott‏ tweeted: "Extremely saddened to hear about the loss of Darlene Horton in London. Ann and I are praying for her family and loved ones."

Dozens of flowers were left at the spot the day after Ms Horton was was killed, one with an American flag and a card "to the family of the American family".

The hearing continues, with sentencing expected to take place tomorrow afternoon.