Jarod saw a chance to take out Aaron, and he took it.
The compartment had very few people from the start, and there were none in the walkway. The cabins prevent not only others from listening to what's going on inside, but they also work in reverse.
When inside, they can't hear what's going on the outside.
As long as it was a surprise attack, no matter what. Jarod believed that this would be the perfect chance for him to complete the mission.
Jarod has to complete the mission, or else there will be consequences for failing to do so. The organization never likes someone who can't complete the mission that they were assigned to.
Aaron was placed at the bottom of the list. So, even if he missed the target, the consequences for failing to complete the mission would not be so bad but in Jardo's case, there was a problem.
Jarod failed a mission not long ago, and if he fails again, it will not end well for him, which he is sure about. So, for him, this is a mission that he can't fail.
