Billy Is in an Interrogation Room at a Police Station

Billy is in an interrogation room at a police station. He was brought there after being arrested on suspicion of DUI. He was not read his Miranda rights on the side of the road when he was taken into custody and was not read his Miranda rights upon arriving at the station either. The detective who enters the interrogation room is unaware of this information and begins questioning Billy about his whereabouts that evening. Billy mentions that he was at a bar called "The Floating Walrus." This piques the detectives interest, because a woman last seen at that bar has been reported missing. When the detective mentions her name, Billy breaks down crying and asks for forgiveness. Billy then says her body is in a wooded area about 250 feet behind the bar. The detective leaves the station, heads to that area, and finds the woman's body; she is dead from a gunshot wound. A gun registered to Billy is lying next to her.
-Let's assume that an appellate court throws out the confession because Billy was not read his Miranda rights. The gun and any DNA evidence found next to the dead body could be considered:

A) Valid evidence derived from a custodial interrogation
B) Fruit of the Poisonous Tree
C) Valid evidence derived from a reasonable suspicion search
D) Admissible in a DUI trial only