How do the members of Border Guard Corps identify the natives of Centrum? They aren't tagged with the circular tattoo which makes it impossible to tell them from random intruders or even smugglers. They also don't speak any Earthly language.
When Becker got the evidence that Agel is the spy, why didn't he simply fill her cell with sleeping gas? She'd have no idea. Even if Striker was in there with at the time, he wouldn't get hurt and Agel would be safely incapacitated and could be taken to interrogation without any complications.