In 5 BBY, Grendahl was onboard the Star Destroyer that briefly captured Adalric Cessius Brandl after he went rogue. Grendahl was first to interview Brandl after the ship he was on, the Kierra was captured. Grendahl was also first to inform Brandl that they would be linking up with the Interrogator. Grendahl then went on to interrogate Thaddeus Ross. After finding no serious infraction, he informed Ross that he would be receiving 10,000 credits for helping to apprehend Brandl. At the end of the interrogation, Admiral Etnam informed Grendahl that Brandl himself would be escorting Ross back to his ship. Grendahl was duly shocked but listened to the command of his superior officer.