As reported by Censor.NET, a law enforcement source told TASS news agency on Thursday.
"A tape from the third black box was found which shows that it was destroyed," the source said.
Despite the tape has been deformed, it may be partly deciphered, according to the source.
"The third black box that was in the tail section duplicates the parameters of the two others that are in Moscow. Its tape has been found and it is seriously deformed but it can be decoded," the source said.
The condition of two flight data recorders - the cockpit voice recorder and the main one (that records parametric data) is satisfactory.
"Their decoding is taking place in Moscow," the source said.
The decoding will be completed soon, according to the source.
At present, all the debris of the Tu-154 plane has been pulled from the water. More than 1,800 fragments of the plane have been found. A total of 19 bodies and 239 body parts have been recovered.
A Russian Defense Ministry Tu-154 plane bound for Syria crashed in the early morning hours of Dec. 25 shortly after taking off from the Black Sea resort city of Sochi. There were 92 people on board the aircraft, including eight crew members and 84 passengers.
The Defense Ministry said that debris from the Tu-154 aircraft were found 1.5 km off the coast of Sochi at a depth of 50-70 meters.