Senior Constable Les Andrew, of Twizel, talks about the horrific crash on July 3, 2017, that claimed the lives of Nigel Freeman and Stephen Hayden. (Video first published in December 2017)

The silver SUV was airborne and tumbling through the fading light.

Senior Constable Les Andrew, watching through the windscreen of his patrol car, knew immediately he was seconds away from a horrific scene.

Nothing in his 26 years in the police could have prepared him for what lay ahead.

JOHN BISSET/STUFF Senior Constable Les Andrew decribes the crash as a "beast".

Andrew was coaching a school basketball team in Twizel when the call came in.

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Several motorists had called police to complain about a silver Toyota Highlander driving erratically, including driving on the wrong side of the road on State Highway 8, which links South Canterbury to Central Otago.

JOHN BISSET/STUFF Andrew saw the silver SUV flipping in the air as he pursued the car.

He eventually found the car on the side of the highway, north of Pukaki, nudged against a fence. The car was still running after the minor prang. Two men sitting inside gave the impression they had been drinking.

The men denied being intoxicated, so Andrew went back to his car to get a breathalyser.

The test showed alcohol.

SUPPLIED Nigel Freeman, 72, died on July 3 in a double-fatal crash near Lake Pukaki.

"I followed normal procedure and then the passenger said 'no, this isn't happening, this isn't going to happen' and started getting a bit revved up."

Realising things were escalating, Andrew retreated to his car to call for help.

"Just as I opened the door I heard the car start up and come towards me . . . then they swung around and took off."

JOHN BISSET/STUFF Les Andrew has been a police officer for 26 years.

By the time Andrew was in pursuit, six cars were between him and the Highlander.

In the distance, he saw it flip.

"It was in the air doing a full rotation.

SUPPLIED Stephen Hayden, 46, died in the crash on July 3.

"I knew it was going to be a fairly horrific scene."

The Highlander had hit a small truck, landing on the side of the road.

On the other side of the road, the truck had gone down a small incline. He recognised the truck immediately. It belonged to Twizel man Nigel Freeman.

"Emotionally for me things started kicking in, knowing it's a local and knowing the other driver was most likely grossly intoxicated.

"I could see bits of car, it was a horrific scene. It was a big scene. One of the worst I'd been to as far as material on the road and the distance it was spread over.."

Andrew checked Freeman, a keen fisherman who set up the Mackenzie Gun Cub in Twizel, thinking he would have had no chance of surviving. He was right.

He then checked the other car. The driver, Australian Stephen John Hayden, 46, was dead. His passenger was seriously injured, but alive.

"From there on some things kicked in as per normal, other things, the emotional things prevented me from being as accurate as I needed to be.

"I think comms and people listening to me could tell that this was affecting me."

He called for help from the police serious crash unit. Local volunteer firefighters, many of whom knew Freeman, arrived shortly after.

"You're sort of trying to ease them down too while you're dealing with the emotions of what's happened. I would describe it as a beast, you wouldn't want too many officers to go through that."

When they arrived, Andrew's colleagues realised he was struggling and took him away. Someone else would handle the crash scene.

The next 48 hours were horrible.

"I couldn't sleep at all, it was just going through my head, your mind's going flatstick and you're thinking of things and you're seeing things, you're seeing the accident, you're seeing Nigel and all that sort of stuff."

All the what ifs did not help.

"If I had done something slightly different. If I had got stuck behind a car or something just changed my timing by a few seconds Nigel would still be here today.

"If I had of just changed one thing . . . Nigel would've got past."

He spoke to a psychologist. First on the phone, then several face to face meetings. After six weeks off work, he was back in uniform.

Andrew recently bumped into Freeman's wife for the first time since the funeral.

"It brings it all back. You think police go do a job and that's the end of it, it's done and it's over with. But when you know the people intimately or have contact with them through the community, it's a wee bit different, the emotional stuff all comes back to you."

Unfortunately such encounters are not unusual for him. In the last three years, two of his former school friends had died in crashes. He was the one to tell their parents.

"They always say 'oh I'm glad you dealt with it Les, I'm glad it wasn't someone we didn't know'. It's really pleasing to know that."

He has learnt a lot from the "beast" – the July 3 crash. Mostly, he is more emotionally vulnerable than he used to be.

"I might not have that again for the rest of my career, but it may happen again tomorrow. You just don't know."