Is there a trope(?) name for minor characters in a TV drama who are introduced early, then forgotten, and then found to be the culprit at the end?

Submitted ⁨⁨2⁩ ⁨weeks⁩ ago⁩ by ⁨bOt@zerobytes.monster⁩ to ⁨television@zerobytes.monster⁩

https://old.reddit.com/r/television/comments/1peg245/is_there_a_trope_name_for_minor_characters_in_a/