Story highlights Russia has exhumed the remains of Czar Nicholas II and his wife in a bid to identify their missing children

Seven members of the Romanov family were killed in 1918, but only five were buried together

In 2007 officials unearthed remains believed to belong to the two children not buried with the czar

Moscow (CNN) Russian investigators say they have exhumed the remains of Czar Nicholas II and his wife, Alexandra, in a bid to identify bone fragments that may belong to two of their children.

Seven members of the Romanov family were killed by Bolshevik revolutionaries in 1918 in the Russian city of Yekaterinburg, a year after they were ousted from power during the Russian Revolution.

The remains of the royal couple, along with three of their five children, were found in 1991 in a mass grave. After being identified with DNA analysis, they were reburied in St. Petersburg on July 17, 1998, the 80th anniversary of their deaths.

The Russian Orthodox Church made them saints in 2000.

But the whereabouts of the czar's two other children -- Crown Prince Alexei, 13, and Grand Duchess Maria, 19 -- remained a mystery until 2007, when their suspected remains, a few bone fragments, were unearthed at a separate grave site in the Urals region.

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