When Lt. Daniels confronts Emerson in his ex-wife's apartment, just after she had been murdered, he hands him a gun wrapped in an evidence bag and asks Emerson if he recognizes it. Emerson admits it is his gun, and Lt. Daniels says that one of his men just found it in Emerson's car. Since Lt. Daniels didn't produce a search warrant the gun should not be admissible as evidence.