If a murder weapon is handed in to a gun buyback program where “no questions asked” is in place, is it inadmissible as evidence if it’s later found to be connected to the murder?

Was watching a short where such a thing happens and the comments were up in flames over it and I got curious.

Edit: the clip in question had the cops go to the station, say they believe it was used in a homicide, and the officer they talk to says “No questions asked means no questions asked”