Warp Talons kill rule?

The Warp talon rule for going back into reserves after killing a unit question.

Do they have to be the ones who specifically kill the entire unit or does the rule not go scgove unless they are the ones who wipe the unit.

E.g. if they charge into a unit along with say some raptors and then its the raptors that end up killing it, do the Warp Talons stay on the board?