Mr Gongadze had been campaigning against government corruption |
Hundreds of Ukrainians are expected to form a candlelit chain on Sunday to mark the anniversary of the murder of a prominent opposition journalist.
Georgiy Gongadze was abducted in Kiev seven years ago. His headless body was later found buried in a forest.
The death triggered a major political scandal and became Ukraine's most high-profile murder case.
President Viktor Yushchenko said finding the killers was a top priority - but no-one has been convicted.
In a related development, another arrest has been made in the murder case of Moscow journalist Anna Politkovskaya.