The teenager who was responsible for a knife attack that killed one woman and injured five others in central London remains in police custody. Authorities have not ruled out terrorism as a motive, and say mental illness is a major line of enquiry.

The attack came the same day as Scotland Yard announced an increase in the number of armed police on London’s streets, in response to the threat posed by terrorism.

The suspect is a 19 year-old man, who attacked his victims with a knife late at night. One woman in her 60s died from her wounds, the others suffered injuries that required hospital treatment.

Significantly, perhaps, the police investigation is being led by Scotland Yard’s Homicide Command, with the counter terrorism unit acting in a support role, suggesting police believe the suspect may be mentally ill as opposed to holding a terrorist motive.

Mark Rowley, assistant commissioner of Metropolitan Police, said, “So far we have found no evidence of radicalization or anything that would suggest the man in our custody was motivated by terrorism.”

The attack comes a day after Scotland Yard announced the number of armed police on the streets of London would increase by 600 to 2,800.

An additional 900-armed officers are planned for the rest of England and Wales. They will be carrying specialist weaponry, including sniper rifles and ballistic shields and helmets. They will patrol the capital’s iconic sites favored by tourists. Although the UK terrorist threat level remains high it is unchanged. Scotland Yard says the new initiative has learned from the atrocities in Nice, Paris and Munich.