The pair work with the highly specialised Collision Investigation and Reconstruction Team, affectionately known as the ''Prang Gang'' within the force.

The team is called out to the worst of the ACT's crashes, using clues gleaned from crushed metal, cracked windscreens, tyre scuff marks, paint fragments and fragile witnesses and victims to map out the fateful seconds leading up to a collision.

Both have become all too familiar with the material carnage of serious crashes.

But it's the human impact of a serious collision - the shattered lives, the emotional trauma and the lingering grief and guilt - that affect the team the most.

Neither hesitates when asked what is the hardest part of the job.

''The death knock,'' says Constable MacKenzie.

''You become more experienced at doing it, but I don't think it gets any easier. While I'm on the way to do it, I'll be steeling myself .. . it's hard.''

The team's long-serving sergeant, Dick Dauth, says that officers do, in some respects, become desensitised to the horrors they see.

He describes it as a professional instinct that allows police to get on with their investigation.

But the emotional drain in knocking on door after door, bringing news of a death that was most likely avoidable, takes a toll.

''Commonly you'll have to take that person who you've just delivered a death message to, so they're not in the best of emotional states, you may then have to take them to … our medical centre at Woden and ask them if they can identify the deceased person for us,'' Sergeant Dauth said.

''Put yourself in the shoes of someone who has that request put on them, they've just been told their mother or son is dead, and then they have to look at them and all the rest of it, it's most unpleasant.''

Unlike most other jurisdictions, an ACT police officer will inform the family and then stay as their main point of contact through the course of the investigation.

This gives the family reassurance, consistency and a sense of trust with police.

The years of experience of Constable MacKenzie and Sergeant Dauth help them to deal with some of the more difficult scenes they encounter.

''You can exclude the things that might have otherwise upset you, at least briefly, for the purpose of getting that task achieved and that job investigated,'' Sergeant Dauth said.