The Dogs of War was about a group of mercenaries hired to depose the leader of a fictional African republic, but certain phrases uttered by the characters were to prove indistinguishable from those spoken by the officers.
Detective Sergeant Martin Kinchin, part of the Northamptonshire Police team investigating Mr Powell's death, and prosecution witness sound expert Professor John French had both analysed the CCTV.
But their lengthy examination failed to include analysis of the film playing in the background of the custody suite.
Det Sgt Kinchin discovered the identity of the movie on the witness stand, the court heard.
Prof French "gave a great deal of ground in cross-examination", said Mr Justice Brown, and agreed to re-examine the evidence.
On his return to the stand, the academic conceded "Gone unconscious" was "formal protest" from Dogs of War.
Sgt Williams' apparent question "How are you doing?" was, he accepted, "Can you hear me?" from the film. The background noise made it difficult to make firm conclusions on what officers said.
Prof French admitted the answer "Dream on" when an officer was asked if Mr Powell was asleep, could be custody cell, "D1".