That fragment with the green clover leaf on it you say your friend recovered appears to be painted on both sides- is it? And is the colour white or cream as it appears to be?
And what makes you think the green piece is a German plane as opposed to an Allied one as the paint would suggest? A photo of the back might help prove it one way or another since I have very detailed photographs and diagrams of every model of Bf109 so should be able to identify it if it is from one.
Ohhhhh- pillage then burn...