When detective Karaman shows Emily the pictures and the sketches of he murdered man, you can see the man stabbed on the left side of the neck on the picture (as really happened), but on the right side of the neck on both sketches.
When Steven and Emily arrive at Emily's family home on the morning after the attack, they are still wearing the same clothes from the night before, have clearly been up all night yet Steven is clean shaven.
While Karaman is questioning Steven in the kitchen, he points out that Steven's footprints are visible all around the body in the blood. We also have seen that when Emily left the kitchen she left a trail of bloody footprints. However, when Steven runs to the door to fix the lock, he miraculously leaves no bloody prints on the floor.
After the scene, where Steven opens a door for policemen, a camera pans down the spiral stairs. You can see two officers down there on the stairs obviously waiting for director's command and then start moving simultaneously.