Filming the killing scene

We have been discussing on how we are going to film the killing. We have realised that this is going to be really hard as we dont know how we are going to make it look like she is stabbing him when obviously she wouldnt be able to get too close to him with the knife. One way we have tried it is filming the shadows of her stabbing him, however this turned out to be really hard as we couldnt work out the right place the lamp should go to make it a good shadow on the opposite wall withought actually getting Aveys hand and the knife in shot not as a shadow aswell.
We have been thinking about it and have decided to get avey to raise her hand with the knife in and bring it down but keeping the camera on her and not showing the victim in shot. We got this idea form Alfred Hitchcock's film 'Psycho'. This is a good way in doing the killing but not actually showing it because it shows that she is killing him but without the audience actually seeing it happen as it would have been very hard for us to shoot it so that it actually looked like her stabbing him if we hadnt done it this way.