Arrrgh! Mission 7 - The Abwehr School - really tough mission

[mbv]

This one is giving me major grief at the moment I may have to restart it. I have both sets of documents and now have to kill the two high ranking officers in the school. I have the officers uniform but simply cannot kill the target in the room off the ground floor lobby that is full of officers and a couple of guards. As soon as you open the door the target identifies you and if you pull out a weapon at all the lobby crowd, and multiple other guards, kill you pretty swiftly. There is no way to distract everyone in the lobby while you kill the target and if you whistle the guards into a side room all of them come to meet you so that you cannot kill them all.

Any tips on how other people approached this one ?