Toilets and seats were trashed, pipework was ripped from the walls and doors were broken in the away fans area, lumbering Swansea with a massive repair bill.
A joint statement by Swansea City and Liberty Stadium managers read: "It is totally unacceptable behaviour and we are extremely disappointed.
"The toilets are now unusable and we are assessing the cost of repairs. It will run into thousands of pounds and Cardiff City are aware of the damage.
"We will be talking to South Wales Police on what measures are being taken to investigate and what improved procedures we can put in place to prevent this sort of unacceptable damage happening in the future."