All, doing a 5 minute freewrite. Thank you for reading.

Criminals no matter how smart they are or how careful they are, they ought to leave a trace somehow on their doings unknowingly. However, this time round for Stuart, there is not a trace of evidence or lead in his investigation on the serial killer whom have already stuck 4 times this month.
It is proving to be a tough case for Stuart to crack. He is convinced that there will be bound to be some form of trace of how this killer operates. Stuart used big data combined with his sharp analysis skills but somehow couldn't find a way out. He then thought to himself, the only way for someone to escape his watchful eyes will probably be due to an insider job whom knew all the action plan and when operations are being carried out.
Stuart devised a plan to test out and find the mole within his team. He started to share plans to all but 1 person for each plan. When something went amiss, he will be able to know who is the one that did not know the information. And through this, indeed the killer was a member of his team and he finally cracked the case.