Original: The "Yurovsky Note," an account of the event filed by Yurovsky to his Bolshevik superiors following the murders, was found in 1989 and detailed in Edvard Radzinsky's 1992 book The Last Tsar.
Simplified: The "Yurovsky Note" was found in 1989 and described in Edvard Radzinsky's 1992 book The Last Tsar. The "Yurovsky Note" was a description of the event by Yurovsky after the execution.