Just done a quick calculation. 400kgs fuel, less ~76kg recovered post crash. 324kgs used in about 110 minutes, so just about 3kg/min average.
Supply tanks generate low fuel warnings at ~30kg in each tank, so with ~60kg there is roughly 20 minutes before flame out on each engine (with a couple of minutes between due to deliberate tank size design).
Those fuel captions must have been lit for that length of time, or a bit longer if in transit rather than in hover where fuel flow would be a bit higher.
Would the two police officers in the crew have observed and understood the fuel captions? Could they see them? I can't imagine they regularly sat and watched the warning display all lit up, so they ought to have known something was not right. Under those circumstances would they not have asked a question or reported it to their colleagues in the control room?
Puzzling!