He helped desperately to resuscitate Ava, rescue his sister who was trapped in the car, and load the family into a rescue helicopter.
He later read the crash report, which laid out how the other driver, 19-year-old Benjamin Farquhar, ended up on the wrong side of the road, crashing head-on into the Hurst family's car.
"He wasn't driving to the conditions. He had sun in his eyes but he carried on at a normal road speed. If he had slowed down to a point where he could see where he was going, it would have never happened," Constable Thomson said.
For him, the crash was a catalyst, he said.
It inspired him to join the police, to try to prevent crashes from happening.
It later inspired him to join the team redeveloping Crash Bash, which aims to teach teens to drive safely.
The annual programme is funded by the city council and NZTA, and will tour a record number of Canterbury schools this year.
Until this year, Constable Thomson said it took a confronting approach, focusing on issues like drink driving by showing the tragic details of crashes involving teenagers.
But it had not been as effective as they hoped.
This year, they have redesigned it to focus on everyday issues - like cornering, following distances and distractions while driving.
To do that, they involved Christchurch teenagers in challenges, some pre-filmed and some done live onstage.
To illustrate the need for a safe, three second following distance, they filmed student drivers asked to follow another car at what they believed was a safe driving distance - and then recorded how far ahead the students skidded when the other car slammed on the brakes.
The programme was then presented live by actors Bianca Seinafo and Josh Johnson from the Court Theatre.
Burnside High School student Nargas Ahmadi, 17, said she believed the message, particularly about distractions, was something she and her friends needed to hear.
She has had her learners licence for about six months but said as a teenager it was easy to slip up.
"We need to be told again and again and again," she said.
The focus of the programme was chosen after examining Canterbury crash statistics.
Between 2012 and 2015, there were about 150 serious crashes in Christchurch which left people injured, and where teen drivers aged between 15 and 19 were partly or fully at fault.
Poor observation was listed as the reason for the crash for about 40 per cent of those crashes.
Constable Thomson's goal was simply to prevent the kind of tragedy his family had to face, he said.
"Every ticket I issue, I look at it as potentially preventing an accident or saving a life," he said.
