Fruit of the poisonous tree (objection) is a legal metaphor in the United States used to describe evidence that is obtained illegally. The logic of the terminology is that if the source (the "tree") of the evidence or evidence itself is tainted, then anything gained (the "fruit") from it is tainted as well.

https://books.google.com/books/about/Fruit_from_a_Poisonous_Tree.html?id=rlBeM-9BOg8C