Who Dunnit ?

In Room 4 we are trying to solve a crime. Someone broke in and tried to steal something but was scared and ran off. They went through a window and we discovered bits of bloody cloth next the broken window. 

First we put the bloody cloth under a microscope and it was real blood. So we watch the CCTV footage and found four suspect

The First suspect was not the one so we  Narrowed it to three so we did the others suspects and here the result

First was AB +

Second, B-

Third, A+ 

Fourth, O-