Georges, Sarah's brother
Suspected because he is a heir on Sarah's will
His story : As he is a lawyer, he was here to help Sarah writing her will. He parked his car in the garage and was greeted by Sarah. They chose a bottle of wine and went to the kitchen to drink it and smoke. They were disturbed by John's birthday party in the living room so they went upstair. They sat in Tom and Sarah's room to write the will. They heard Five gunshots. Sarah ran in the corridor. He heard her getting shot. He got scared and blocked the door with his chair. The killer tried to open the door, then went away.
I don't trust him !