Investigators have opened the coffin of Russia's next-to-last czar to obtain genetic material from his remains and say it was not tampered with in Soviet times.

The coffin of Alexander III, in the cathedral in St. Petersburg's Petropavlovsky fort, was opened Friday as part of an attempt to identify what may be the remains of his grandchildren, who were killed by the Bolsheviks.

Alexander III died in 1894, passing the throne on to son Nicholas II. Nicholas and his family were executed in 1918.

Remains believed to be those of Czarevich Alexei, the heir to the throne, and one of his sisters were to have been buried this year. But the Russian Orthodox Church, which has canonized all of Nicholas' family, has asked for further genetic examinations.