The city council said it intended to recover costs from the theatre's owner
The owner of Derby's derelict Hippodrome theatre has pleaded guilty to carrying out work on the building without the right permission.
Developer Christopher Anthony, of Bishops Stortford, ordered work on the Grade II listed building two years ago which led to it being damaged.
But the judge at Derby Crown Court agreed Mr Anthony did not cause the damage for financial gain.
Sentencing will take place sometime in April at Stoke Crown Court.
Contractor Wayne Watson had all charges against him dropped after the city council's legal team offered no evidence.
Part of the roof and outside walls collapsed as contractors worked on the building in March 2008.
The court heard the damage was not deliberate but it was rather a "botched job".
The main part of the venue, which dates from the early 20th Century, has been open to the elements ever since and has been damaged by two fires.
In a statement Derby City Council said it was happy Mr Anthony had admitted his guilt.
It added a lot of money had been spent securing the building and protecting it from trespassers, and steps would be taken to recover the costs from Mr Anthony.
A plan to convert the area into a car park will go before city council planners in the next few months.