The State Opposition is questioning why sabotage charges have been dropped against some of those behind the biggest prison riot in Victoria’s history.

Prosecutors have reached a plea deal which will instead see three inmates plead guilty to a riot charge over the incident at the Metropolitan Remand Centre last June.

But Shadow Corrections Minister Edward O’Donohue said those responsible needed to be adequately punished.

‘The cost has escalated to more than $95 million and no doubt the cost of the court cases will grow that even more,’ he told 3AW News.

‘Daniel Andrews needs to explain how this occurred and guarantee how it won’t happen again in future.’