How many letters does the top answer for “a police investigation to determine the perpetrator” have?

The most common answer is detecting (9 letters).

Crossword clue: a police investigation to determine the perpetrator

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

detecting 9 letters wn-def

a police investigation to determine the perpetrator

sleuthing 9 letters wn-def

a police investigation to determine the perpetrator