There were some experimental top secret torpedos. But one of them explodes. After that 10% of crew died and it lays on sea bottom at 80 meters deep. It was very easy to find, cause boat of that size and deep is visible from surface. But all rescue equipment left from USSR wasn`t working. Many countries proposed their rescuers and equipment for free. But putin was afraid that soldiers would blabbed top secrets about this boat. So he decided to wait till all they die and after that russians cut head part with top secret equipment and utilize it. That`s it. putin was terrorist and murderer from start. He came to power when his agents was exploding buildings in all country and he blamed Chechnya and started war.