A Northern Ireland man who witnessed the aftermath of a "spontaneous" knife rampage in London, that killed an American woman in her 60s and wounded five others, has spoken of the horrifying ordeal.
The attack happened on Wednesday at around 10.30pm in the Russell Square area of the city.
A 19-year-old man, a Norwegian national of Somali origin, has been arrested on suspicion of murder.
Paul O Geibheannaigh - a London resident for 12 years - said he had not seen such a heavy police presence since the 7/7 attacks.
"I was out at the cinema when we stumbled across what was a heavily armed police presence in Russell Square - and then we saw the body lying on the pavement, which was quite disconcerting as it was not covered at the time," he told the BBC.
"Then we went for a late night drink with a friend and everyone was in shock in the bar. Then the police came in and interviewed us and at that stage we didn't know there were others injured.
"At first we thought it was gang-related.
"There was a massive police presence - I have not seen a police presence like it since 7/7. And that just brought those memories back.
"You don't really see that in central London. There must have been 70 or 80 police officers, all carrying sub machine guns."
The American woman who died was named last night as Darlene Horton (64).
A post-mortem examination was to take place today at St Pancras Mortuary.
Florida State University (FSU) has confirmed that Ms Horton was the wife of psychology professor Richard Wagner.
It's also reported that a British man was stabbed in the stomach and remains in hospital in a "serious but stable" condition.
Four other victims have been released from hospital; an American man stabbed in the chest, an Australian woman stabbed in the back, an Australian man stabbed in his chest and an Israeli woman stabbed in her arm.
Speaking yesterday outside Scotland Yard, Assistant Commissioner Mark Rowley said: "While the investigation is not yet complete, all of the work we have done so far increasingly points to this tragic incident as having been triggered by mental health issues.
"At this time, we believe this was a spontaneous attack and that the victims were selected at random."
Mr Rowley, Britain's most senior counter-terrorism officer, added: "I emphasise that so far we have found no evidence of radicalisation that would suggest the man in our custody is in any way motivated by terrorism."
He said "urgent progress" had been made in five areas of the investigation: interviewing the suspect, speaking with his family, witness accounts, address searches and a full intelligence review by police and security services.
A spokesman for Norway's Ministry of Foreign Affairs has confirmed that the unidentified attacker emigrated from Norway in 2002.
Matthew Barzun, US ambassador to the UK, has tweeted his condolences: "Heartbreaking news that a US citizen was killed in #RussellSquare attack. My prayers are with all the victims and their loved ones."