You should probably give some more details on what you mean. Do you mean how long would they avoid getting caught? Depends entirely on how they use it. Light Yagami made himself too obvious by constantly offing every criminal talked about on his local news. The smarter move would have been to use it sparingly. Off a dictator every few months or so in a way that doesn’t look like they’re connected.

“No Mr. FBI Sir. I do not posess a ‘Death Note’ and Kira is obviously evil!”

turns around

pulls out piece of paper

bites finger

writes “Raye Penber” with blood