One problem with this being an open ended mystery, like Columbo

Knowing who the traitor is from the start, I keep wanting to yell at the other agents who can't see it, especially when Grimes keep telling them he's the mole and they don't listen. Innocent until proven guilty is for the trial, not the investigation.

G.K. Chesteron wrote in one of his Father Brown mystries that the biggest flaw with a lie detection machine is the operator's assumptions.