Piri was one of the real bombers behind the attack for which Harry Kim and Tom Paris were imprisoned on Akritiri.
Piri was an Akritirian who, together with her accomplice Vel, carried out the trilithium bombing that the Akritirian authorities blamed on Harry Kim and Tom Paris.
In The Chute, Voyager's crew tracked down and captured Piri and Vel. When the Akritirian ambassador refused to release Kim and Paris even with the true culprits in hand, Janeway struck a deal with the bombers, freeing them in exchange for information on the location of the hidden prison and how to break into it. That knowledge let Janeway lead the rescue that brought her officers home.