Three people were stabbed to death in a "terrorist incident" at a park in a town just outside London on Saturday, police said. Three others were left seriously injured in the attack.
The attack took place in Forbury Gardens, a public park in Reading, a large town around 40 miles west of London, at around 7 p.m. local time (2 p.m. ET), Thames Valley Police said in a statement shortly after the incident.
Personal trainer Lawrence Wort told Britain's Press Association news agency that the park was full of groups sitting on the grass when “one lone person walked through."
He said that the person "suddenly shouted some unintelligible words and went around a large group of around 10, trying to stab them.”
He added: “He stabbed three of them severely in the neck and under the arms, and then turned and started running towards me, and we turned and started running."
Shortly after the incident, a 25-year-old man from Reading was arrested on suspicion of murder, police said, adding that they were not looking for any other suspects. The man's name was not released.
One of the victims was identified as teacher James Furlong, according to a statement from The Holt School in Wokingham. Furlong served as the Head of History and Government and Politics at the school, where he was determined that students would gain critical awareness of global issues, the statement said.
“James was a very kind and gentle man; he had a real sense of duty and cared for each and every one of our students," the statement said. "He truly inspired everyone he taught through his passion for his subject and his dedication. "
Thames Valley Police said that the attack was not connected to a Black Lives Matter rally, as the stabbings happened around three hours later.
The force initially said the incident was not being treated as terrorism. But that assessment was changed after they worked with Counter Terrorism Police.
The stabbing was later declared a "terrorist incident."
Neil Basu, head of U.K.'s Counter Terrorism Police, called it “an atrocity,” at a news conference Sunday.
“My deepest sympathies go out to the families who will be mourning loved ones today after this horrific act and to everyone who has been affected by it,” he said, before thanking the officers who stopped the attacker and members of the public who provided emergency first aid at the scene.
Basu reiterated that the incident was not associated in any way with the earlier Black Lives Matter protest.
Detective Chief Superintendent Kath Barnes with the Counter Terrorism Police said Sunday that the investigation was moving at a fast pace.
“We know that the suspect entered into Forbury Gardens in the centre of Reading and attacked members of the public with a knife leaving three people dead and three people needing hospital treatment," Barnes said.
In a separate statement, Chief Constable John Campbell of Thames Valley Police said he was "deeply saddened" by the stabbing, which he called a "tragic incident."
“Incidents of this nature are very rare, though I know that will be of little comfort to those involved and understand the concern that this incident will have caused amongst our local community," he added.
Campbell described the scene as "pretty horrific" and noted there was a number of civilians who were witness to the event.
"We also had a number of people in the park that were witnesses to this incident and then saw the terrible, terrible tragedy unfold," Campbell said. "So you can imagine both my officers, but also for those that were involved, it's very distressing."
The chief constable asked that anyone who has video or photos from the incident refrain from posting the images to social media and instead submit them to the authorities.
Prime Minister Boris Johnson tweeted that his thoughts were with those affected by the attack, adding Sunday that he was "appalled and sickened that people should lose their lives in this way."