CNN conducted an interview with a forensic criminologist that highlights how police officers train for situations with a threatening assailant, including when an assailant may be some distance from the officer.

Mock scenarios show that if a police officer and an assailant are 21-feet apart, the officer has no time advantage in getting his gun out and lifted. It takes 2 seconds to do that. And those 2 seconds do not include aiming. On average, in 2 seconds an assailant who is 21-feet away would be able to traverse the distance and reach the officer.

And this does not take into account the multitude of variables in real life situations such as the officer’s adrenaline, facing more than one assailant, or civilians in the area who could get injured, among other factors.

Distance matters. It will undoubtedly be an element in the case of the fatal shooting of Michael Brown – an extremely large man who appears to have attacked Officer Darren Wilson.