Updated

LONDON -- A British woman who allegedly stabbed a complete stranger to death in a London street left a mental health unit just over one hour earlier, it was disclosed Tuesday.

The 31-year-old was admitted into Oxleas House in Woolwich, southeast London, on Monday after she asked to be held under the Mental Health Act but left the unit while staff were preparing a bed and medication for her, the London Evening Standard reported.

She was pursued by staff but managed to leave the site in a cab. Around 90 minutes later, the woman was arrested on suspicion of murder after allegedly stabbing Sally Hodkin, 59, in a random attack in front of shoppers in nearby Bexleyheath.

A spokesman for Oxleas NHS Foundation Trust said, "At Oxleas House, she was promptly assessed. A bed was available and medication was being prepared before admitting her to a ward on a voluntary basis. At 7:00am [local time], she unexpectedly left the assessment suite and was pursued by staff."

He added, "Up to this point, she had not given any indication she intended to leave and had agreed to admission. She was seen getting into a taxi and left the site. Staff took the number of the taxi and subsequently notified the police."

Hodkin, a grandmother who worked as an accounts manager for a local law firm, was pronounced dead at the scene after being stabbed in the neck.

Moments earlier, the attacker used a knife that she bought from an Asda supermarket to injure 23-year-old Kerry Clark, who was waiting at a bus stop, Sky News reported. The suspect was disarmed but ran off and stole a steak knife from a butcher's shop before threatening to stab a staff member and attacking Hodkin.

Witnesses said the woman then ran into a tile shop and told manager Ryan Higgins that she was "supposed to have been sectioned last night" and "wanted her medicine."

Higgins, 32, said, "She came through the front door and said, 'I've hurt somebody. I think I've killed them,' and that I needed to call the police. As I dialed 999, I reached for the first aid kit from the back door because she had deep cuts on her fingers of her left hand, and there was a lot of blood. Then she walked out to the parking lot, where the cops were waiting for her."

He added, "She was shocked and really quite upset. She was really panicky and started crying when she got outside. I could hear her saying to the officers, 'I did it, I did it.'"

Nicola Edgington, 31, of Greenwich, was charged with murder and attempted murder. She was judged unfit to attend Greenwich magistrates court Tuesday morning.