Last week two of my relatives were travelling in a group which was involved in a road accident. One was unharmed and the other was slightly injured, but several members of the group were more seriously injured and one was killed. I told my wife this, emphasising that my relatives were safe before concluding “One of their friends was killed”. She asked “Someone killed him?”
Passive voice he was killed (by someone or something) has the active voice equivalent (someone or something) killed him. But we can’t say The accident killed him or even He was killed by the accident (or we can, but they sound really strange), but might say He was killed in the accident and certainly later say He was killed in an accident.
I might have avoided the confusion by saying One of their friends died.