One of the most frustrating cases I’d dealt with was that of a drug baron named Leon Fawkes who was acquitted of three gangland murders even though we knew he’d committed them. Each case fell apart because we failed to come up with sufficient evidence to convince the juries.

That was where we stood with Roy Slack. It was why I feared that there might be only one way to stop the killings – and that was for someone to take the law into their own hands.

I was also pretty sure that I wasn’t the only copper in the Met who was coming to the same conclusion in the wake of the Commissioner’s murder.

At 8am I went to the waiting room to check on the news.

I quickly discovered that quite a lot had happened overnight.

Detectives had established with a high degree of certainty that the sniper was indeed a woman, and that she had fired on Appleton Mews from a room on the fifteenth floor of the Sky Reach Hotel.

There was even security footage from inside the hotel of her walking up to reception and checking in. Predictably she kept her head down and avoided looking at the camera. But I didn’t need to see her face to know that she was the same woman who had shot Aidan. She had simply swapped her motorbike leathers for a dark raincoat, which she wore with the collar up.

There was also something not quite right about the blonde hair, which led me and others to believe that it was a wig.

A DCI Maurice Longford was interviewed by reporters outside the hotel and made an appeal for anyone who had seen the mystery woman to come forward.

‘A number of factors lead us to believe that she’s the assassin,’ he said. ‘She checked into the hotel a few hours before the Commissioner was shot and requested a room on the fifteenth floor facing Appleton Mews. She then vacated the room directly after the shooting and was seen leaving the hotel. We now know that the credit card that she used at check-in was a fake and the address she gave does not exist.’

I switched between the news channels. On Sky a reporter did a piece-to-camera outside 10 Downing Street and explained that the COBRA emergency committee would be meeting there soon to discuss how to deal with what was happening.

CNN carried an interview with the Mayor of London who described the death of the Commissioner as devastating.

‘This sustained attack on the Metropolitan Police is without precedent,’ he said. ‘The investigation into the shootings and the threats that have been made is now the biggest of its kind ever undertaken in London. During the night, officers carried out raids on dozens of homes and a number of arrests were made. We’re confident that inquiries will lead to the apprehension of the assassin and whoever she’s working with.’