The death penalty should be reinstated for people who kill police following the murder of Pc Sharon Beshenivsky, the former Met Police chief has said.
Lord Stevens is credited with turning around the fortunes of the Met
Lord Stevens said the "cold-blooded" murder of Pc Beshenivsky had "finally" changed his mind on the death penalty.
"Such an extreme act of pure evil can only be met by the most extreme of responses - and that can only be death," he told the News of the World.
Pc Beshenivsky was fatally shot outside a travel agents in Bradford.
"All my life I've been against the death penalty," Lord Stevens said.
"I genuinely never thought I'd say this, but I am now convinced that the monster who executed this young woman in cold blood should, in turn, be killed as punishment for his crime.
"For the first time in my life, despite 40 years at the sharp end of policing, I finally see no alternative."
If the death penalty was not imposed then "wrong really has finally totally triumphed over right and all civilised society, all we hold dear, is the loser," he added.
He said there must be "massive safeguards" to make sure there were no miscarriages of justice in imposing the death penalty.
"But those who can incontrovertibly be proved to have murdered a police officer should be killed," he said.
Murdering someone who you knew to be a police officer was different from all other murders.
"You are not just killing an individual, you are attacking everything they represent," he added.
"I know now that capital punishment is the only major way left for the majority of right-thinking people to fight against the minority of monsters in our midst.
"I'm just so sorry yet another brave police officer has had to be murdered before it happens."
Lord Stevens was head of the Met from 2000 until January of this year.
He is widely credited as turning around the fortunes of the force following the Macpherson Report which said it was "institutionally racist".