That scene came two times in the film, first in the start and second time in the climax.
In the first time of that scene, we did see him taking those blue liquid packs which were used to make more Winter Soldiers later on from the car.
When that scene came back again in the climax, we only see him murdering Tony Stark's parents.
But we can connect the dots, that Stark's parents were preventing that experimentation maybe they knew about S.H.I.E.L.D.'s infiltration by Hydra and also about the Winter Soldier program, that's why they were on some kind of run.
And as he was told to leave no eye-witness, he killed Stark's parents.
Even his death was mentioned in Captain America: The Winter Soldier with the involvement of Winter Soldier and Hydra: