As an investigator, I used eye-blocking behaviors to assist in the arson investigation of a tragic hotel fire in Puerto Rico that claimed ninety-seven lives. A security guard came under immediate suspicion because the blaze broke out in an area where he was assigned. One of the ways we determined he had nothing to do with starting the fire was by asking him some very specific questions as to where he was before the fire, at the time of the fire, and whether or not he set the fire. After each question I observed his face for any telltale signs of eye-block behavior. His eyes blocked only when questioned about where he was when the fire started. Oddly, in contrast, he did not seem troubled by the question, “Did you set the fire?” This told me the real issue was his location at the time of the fire, not his possible involvement in setting the fire. He was questioned further on this topic by the lead investigators and eventually admitted to leaving his post to visit his girlfriend, who also worked at the hotel. Unfor- tunately, while he was gone, the arsonists entered the area he should have been guarding and started the fire.