As he proudly showed off the latest arsenal intended to combat terrorism, Scotland Yard Commissioner Sir Bernard Hogan-Howe warned Londoners on Wednesday that it would only be a matter of time before the capital suffered an attack.
Just hours later his warning appeared chillingly prophetic when a knifeman went on a rampage in Russell Square, central London, killing an American woman in her 60s and wounding two Australians, an Israeli, an American and a Briton.
Armed officers were on the scene within minutes and the attacker was subdued with a Taser and arrested. Within hours Scotland Yard confirmed terrorism was a major line of inquiry.
Asst Commissioner Mark Rowley, the Met's anti-terror chief, even appeared before the cameras outside New Scotland Yard in the early hours of the morning setting out what his officers were doing to investigate possible extremist connections.
Sadiq Khan, the Mayor of London, cut short a family holiday in the Mediterranean to fly back to deal with the incident. But by lunchtime yesterday any terrorism link had been discounted after officers said the 19-year-old Norwegian attacker, of Somali origin, had not been radicalised and had been suffering from a mental health condition.
Sources in the United States named the attacker as Zacharia Bulhan, although Scotland Yard refused to confirm his identity.
The Norwegian foreign ministry confirmed that the attacker had moved to Britain when he was five and he was thought to live in north London.
The tragic sequence of events served to demonstrate the effectiveness and professionalism of the officers who respond to such incidents.
But it also highlighted the tension and fear that continues to grip the country in the wake of a string of terrorist outrages across Europe.
The incident began shortly after 10.30pm in the popular Bloomsbury area of the capital not far from the British Museum. Russell Square was busy with holidaymakers and visitors many returning to their hotel rooms following a night out.
Without warning, a knife-wielding man, wearing a white T-shirt and black shorts, is said to have begun slashing and stabbing at passers-by. In a few bewildering moments six people lay with stab wounds as onlookers called the emergency services on their phones.
A cyclist passing the scene moments after the stabbings said he was flagged down for help by a Spanish family.
The 40-year-old Brazilian, known as Fernando, said: "The moment the police arrived, they asked them if the man had been shouting. They said that he didn't say anything. They said that when he stabbed the people he didn't shout or scream anything."
Jodie Parry who was in her hotel room overlooking the scene said the alleged attacker fled, ignoring police demands for him to stop. She said: "He was actually carrying a knife in his hand and he had blood on his hands."
The American woman killed in the attack was Darlene Horton.
The Tallahasee Democrat said Mrs Horton had been in London with her husband, Richard Wagner, a psychology professor at Florida State University, who was visiting Britain for a summer study abroad programme. The couple had reportedly been due to return to America yesterday.
The five injured victims were taken to hospital. Last night the British victim, who received a stab wound to his stomach remained in hospital in a serious but stable condition.
The four others: an American man who was stabbed in the chest, an Australian woman stabbed in the back, an Australian man who received a stab wound to his chest and an Israeli woman who was knifed in the arm, were all discharged from hospital.
Yovel Levkowki, 18, an Israeli holidaymaker who was slashed across the hand, described how she tried to help the dying woman. She said: "I was afraid it was a terrorist incident and I was sure that the two men fleeing from the event were victims.
"I went to help the first one of the men and felt pain in my hand. I thought I just got hit, but it turned out he was stabbing me. The other man chasing him was trying to stop him, and in the end managed to catch him." She told Israeli media: "I saw a woman lying on the floor, covered in blood. Her husband was supporting her."
In a statement Mr Rowley said there was no indication that terrorism had played any part in the attack. He said: "Whilst the investigation is not yet complete, all of the work that 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 the victims were selected at random."
He added: "So far we have found no evidence of radicalisation or anything that would suggest the man in our custody was motivated by terrorism." Mr Rowley also defended the decision to refer to the incident as a possible terrorist attack, insisting that in the current climate all options had to be kept open.
On Wednesday the Metropolitan Police publicly displayed some of its latest anti-terror kit. Sir Bernard said more officers would be on the streets to reassure the public and keep them safe.
Sir Bernard said: "My thoughts are with the family of the woman who was murdered and those who were injured. A normal night out in our busy capital has ended in horrific circumstances."
He continued: "Across our capital today you will see more police officers, armed and unarmed, to reassure the public after recent events overseas. We will protect our capital and those who live, work and visit our city."
Mr Khan urged Londoners to remain "calm and vigilant".