Would you kill somebody if he/she asks you to do it?

If you watched A million dollar baby than you know exactly what am I trying to ask but if you don’t here are the details:
You have a friend/relative who lived his/her life(he got a shot to let something behind)and he got severely injured.He is conscious but he can’t even breath alone.So he is bound to a bed and to lots of wires in a small depressing room.He gets increasingly unhappy with his ’‘new life’’ so he decides that he doesn’t have to ’‘live’’ like this anymore.He can’t legally ask to be killed so he asks you to disconnect him from his life supporting machines.
Would you do this?(Why?)Would it be easier for you to do it if it was a close friend or a casual one?
How would you continue your life if you choose to do this thing?