The woman stabbed to death in an attack on a street in London was the wife of a Florida State University psychology professor.
Darlene Horton, 64, was killed when a Somali-Norwegian teenager went on a knife rampage Wednesday through Russell Square, a hub for students and tourists.
London police Thursday said they found no evidence of radicalization to suggest terrorism in the attack that wounded five other people — two Australians, an Israeli, an American and a British citizen, none with life-threatening injuries.
Instead, police say the attack was likely triggered by mental health issues.
Police arrested the 19-year-old man after incapacitating him with a Taser. The man — who has yet to be publicly named — is in police custody at a nearby hospital.
U.S. Secretary of State John Kerry described the attack as a "horrific mass stabbing," and said he grieves for the victims.
The knife attack came the same day London officials announced an increase in armed police patrolling the city, in an effort to prevent terror attacks.
Dubbed "Operation Hercules," the boost in officers carrying guns is a response to the stepped up terror attacks in Europe recently, according to police officials.
"In some of our big iconic locations, we've already got armed patrols — if you look at Parliament, Downing Street — so it's not entirely new," Metropolitan Police Chief Bernard Hogan-Howe said. "I think people understand that, where you are going to have people as enemies who've got guns, we've got to have guns."
WATCH: US Secretary of State John Kerry comments on stabbing
The decision to put armed police on the streets in London is significant because the vast majority of officers in Britain do not carry firearms — a standard that will remain intact for most of London's 31,000 police officers.
Mark Rowley, the Metropolitan Police Service's Assistant Commissioner for Specialist Operations, said police believe the mental health of the suspect to be a "significant factor" in the case, but cautioned that it is just one of several lines of inquiry.
Police received a call about the attack in progress around 10:30 p.m. local time, and within about 10 minutes had arrived on the scene and subdued the attacker.
"Anyone who's been following events in Europe over the past few weeks will understand why we want to show our determination to protect the public," Hogan-Howe said. "We are deadly serious about the protection that we are offering the people of London and we will never be complacent."
In a statement, London's Sadiq Khan, the first Muslim mayor of a major Western capital, said safety in London is his number one priority, and he expressed condolences for the victims of the attack.