The audit office has conducted a spot check of the museum’s collections and in a new report published on Wednesday states that of the 100 selected items, 12 cases of negligence were found.

The most serious error was that the Andy Warhol lithograph “Jade white butterfly” was nowhere to be found.

“We regard this as very serious and are doing all that we can to clarify what has happened. We have not found the work, but we are working intensively with the matter,” said Lars Turesson, head of the museum’s administration department, to the newspaper in a comment on the report.

The lithograph formed part of a book featuring 62 works by 28 artists which, according to the Expressen daily, is worth up to around 35,000 kronor ($4,400).

The museum has also been criticised for not conducting an annual audit of its collections and for having lent three works without registration as well as ahaving a number of unregistered items in its collections.

The museum now has until June 19th to submit a formal response to the National Audit Office report and Lars Turesson was unwilling to comment further on the details of the criticism or the museum’s work to address the issues raised.