Re: Huh?
He should be liable for the whole amount, the debt was incurred in good faith by the company he was working through and the government lost the full amount. If the Subcontracting companies do repay their profit margin less overheads and costs of investigation that could be taken off his debt but the investigation costs may actually increase his debt if that approach is taken.
But what kind of idiot attempts time fraud in a secure environment. I remember combating this back in the 90's purely by using system login details and phone logs, we had a contractor working on another contract on our time, contrary to the agreed work plan.
I suspect this was as simple as he was claiming for whole periods when he wasn't on site and a supervising manager just called the facilities department and asked for the access logs. No other technology was needed. If he wasn't on-site he couldn't be working.