"Don't shoot," the gunman begs me as I train my firearm at his head.
Hands raised, he drops his weapon to the floor - then from nowhere whips out a second pistol, aiming it at me.
No time for a warning, I squeeze the trigger and hope my reactions are quicker than his. I feel like Clint Eastwood in Dirty Harry.
Thankfully, my assailant is no more than an image of an actor on a screen. I am taking part in New Scotland Yard's latest scheme to give the public an insight into the split-second decisions taken by specialist firearms officers.
'Sound judgement'
Using the same laser guns and simulated ranges as the Metropolitan Police's elite CO19 squad, volunteers can test their judgement as they decide whether to shoot armed suspects.
Just like trainee officers, those taking part test their nerve and reflexes in a range of scenarios including bank raids and hostage standoffs.
The initiative comes after the unit was subject to enormous scrutiny following the controversial killings of Jean Charles de Menezes and Harry Stanley by police marksmen, and the wounding of Mohammed Abdulkahar during a raid in Forest Gate.
Ch Supt Bill Tillbrook, the officer in command of C019, denies that the scheme was prompted by the shootings.
"There are misconceptions about what we do and why we do it"
He says: "This is not a response to any particular incident.
"But what the publicity and the public reaction to those incidents show is that there are misconceptions about what we do and why we do it.
"I don't expect everyone to support us. But I would like them to properly understand what it is we do."
Ch Supt Tillbrook adds that the two most important qualities he looks for in a firearms officer are ability to handle a weapon well, and sound judgement.
From January to October 2006, he says his officers were called to 10,000 incidents, but only opened fire on three occasions.
'Under pressure'
Debate about the role of armed officers refuses to go away. Last month Robert Haines, 41, was shot dead by CO19 officers in Kent by the same officer who killed Mr de Menezes.
Just last week police were told they could face disciplinary hearings in public when they are accused of serious incompetence or neglect. This would mean officers being compelled to justify split-second decisions in front of victims, their families and the press.
I put myself in a marksman's shoes as Sgt Paul Anjos talks me through my turn on the firing range. He tells me to stand upright and hold my gun firmly with both hands.
When the suspect on the screen in front of me starts firing, I let off five rounds.
When I drop my gun, Sgt Anjos grills me about the man I have just shot. What was he wearing? What exactly did he say? What did he look like?
I cannot remember.
This is called perception distortion, Sgt Anjos tells me. "When someone is under pressure they often don't notice simple details because they are so focused on the task in hand."
For this reason, he says, firearms officers are given 24 hours before they have to write up reports of operations, to allow time for their sense of perspective to return.
The simulation is now available for use by Police and Community Consultative Groups, forums in which members of the public liaise with police.
I put down my laser gun and walk away from the range, relieved that my moment of power over life and death was only an illusion.
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