term:

Evidentiary Harpoon

evidentiary harpoon n

[from the comparison of such evidence to a harpoon, which can be retracted after it has injured its target]
: evidence consisting esp. of a police officer's statement that is improper and is knowingly offered by the prosecution to prejudice the defendant in the eyes of the jury

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.