Bryukhanov also found a letter written by one of the Kurchatov Institute experts, which revealed the perilous design faults that were kept hidden from him and his staff for 16 years.[2] On 20 January 1987, after he sat in isolation for six weeks, the prosecutor's office filed their closing indictment with the Supreme Court of USSR. All of the 48 files of evidence sent to Moscow were classified top secret.[2]