Walker Behind Train
 

Behind the train, a walker is strapped into a car. I cannot shoot it (too loud) and no melee weapon from the train kills it. If I unbuckle its seat belt, I still can’t kill it. How does one kill this particular walker?

u kill it by slamming the door on his head when the walker comes near u (after unbuckling the seat belt). Pointer should be on the handle of the car door.