Mutation

One evening, an ordinary middle aged man Wahid returned to his home and with full of surprise, he noticed a stranger sitting with knife in his hand.
When the stranger threatened Wahid, he tried to recollect his entire life whether he (Wahid) had any severe enmity with someone that the enemy would try to kill him now!

But the stranger assured Wahid that he didn't come here to kill Wahid. Rather, he assigned Wahid a job to kill a man and that murder should be committed immediately.

As an innocent man, would Wahid be able to kill a man brutally? Or is Wahid not an innocent man, rather he is a killing machine who kills everyday to survive??