Although newspapers reported that a murder victim had been stabbed with a knife, two police investigators knew that the actual murder weapon was a letter opener. while carefully monitoring the changes in the heart rate and perspiration level of a prime suspect, the investigators asked him if he typically used a letter opener on his mail. the investigators were making use of

guilty knowledge test

Explanation:

Guilty knowledge test: The guilty knowledge test is also denoted as GKT, and is referred to as the psycho-physiological questioning technique which is being utilized as a part of the polygraph examination that assesses the suspects in terms of concealing guilty knowledge through measuring his or her physiological response while performing a specific series of a few multiple-choice questions.

The given statement in the question signifies that the investigators were using the guilty knowledge test.

is this supposed to be a question