NCA deputy director general Phil Gormley said the scale of offending discovered by the child abuse operation was "shocking".
His colleague, chief constable Simon Bailey, said the number of indecent images of children has risen from under 10,000 in the 1990s to a figure in the tens of millions today.
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The Police Federation chairman said officers were often "letting someone off with a warning and hoping for the best".
A total of 21 are also injured by a blaze which ripped through the upmarket 22-storey hotel on the Black Sea coast.