1. It is given by the directions that every statement in the second interview is true.
2. The third interview contains “By the time these interviews get published, everything in them will be a lie.” For this to be true would require it to be false, but it can simply be false. At least some of the information in the third interview is false.
3. Because the second suspect is certain about what the person who bought pizza will say, the person who bought pizza either always tells the truth or always lies.
4. The freshman must lie at least some of the time because they told the second suspect that everything they say is a lie. (This cannot be true for the same reason shown in step 2)
5. The first suspect claims they “didn’t say anything this morning that would contradict itself if it were true,” hinting that they expected someone else to accuse them of it. This would be a pointless thing to say if it were true, and it being false lines up with the second suspect’s claim about what the freshman told them. The only way this would happen is if the first person is the freshman.
6. The first and third interviews both contain lies, and the second interview says that two people always tell the truth. The fourth interview must only contain the truth.
7. The fourth interview states that “People younger than me have told you four relevant lies.” Everyone makes more than four claims, and the freshman, who is younger than everyone else, can lie. The freshman must tell some truth and some lies.
8. The second interview says that at least one person always lies. That can only be the third interview.
9. The third suspect said, “Someone older than me can tell the truth.” Because the other three people can tell the truth, this can only be a lie if the third person is the senior.
10. (My favorite clue) The third suspect says that “the sophomore told you the truth.” This must be false, but only the freshman and senior can lie. The only possibility is for the interviewer to not have spoken with the sophomore yet, as the use of the past tense “told” would then make that statement false. The fourth interview must then be the sophomore.
11. By process of elimination, the second interview is the junior.

At this point, you know the grade of each suspect and whether they tell the truth:

First is a freshman and mixed.

Second is junior and true.

Third is senior and false.

Fourth is a sophomore and true.

1. The fourth interview says that “someone showed off a kinematics problem at the start of the math and logic club.” The math and logic club takes place during lunch. The first suspect claims that they did the kinematics problem, but their interview started at 10:32, meaning they were talking to the investigator at the start of lunch. This is one of the freshman’s four lies.
2. The freshman claims to be going to the pizza place. Freshmen do not go to the pizza place. This is another of their four lies.
3. The fourth interview is taken at 2:20 p.m. (written as 14:20) which is during tenth period. The sophomore says, “it got warm out here,” meaning that they are not in a building and by extension not at an Outlook meeting. They also claim to go to every meeting, so if they are outside there is not a meeting at that time.
4. In the first interview, the freshman claims that the Outlook meeting is tenth period on the same day. This is another of the four lies. (On the website, this statement is not bold. The printed version is correct.)
5. The freshman’s claim that they “didn’t say anything this morning that would contradict itself if it were true” makes four lies, meaning anything else they say is true.
6. The freshman’s claim that “the guy who did the torque problem will confess that he touched the board” is true.
7. The junior in the second interview comments on the school lunch. The senior in the third interview, the only other suspect allowed to leave the school during lunch, must have been the one to get pizza. The junior says that the senior was at the math and logic club when they got there, but they could have gotten pizza if they left soon after or had a priv.
8. The sophomore in the fourth interview says that the person who did the circuit problem went to get pizza, meaning the senior in the third interview did the circuit problem.
9. The sophomore in the fourth interview said, “I heard from someone else in my grade that someone showed off a kinematics problem at the start of the math and logic club, but I wasn’t there.” The freshman in the first interview was also not present at the start of the math and logic club (see 12), meaning the junior in the second interview must have been the person to do the kinematics problem and show it to the club.
10. The sophomore in the fourth interview said that “the person who did the momentum problem is younger than the person who did the torque problem.” The only two people without known problem types are the freshman in the first interview and the sophomore in the fourth, meaning the freshman did the momentum problem and the sophomore did the torque problem.
11. The sophomore in the fourth interview would, if asked, confess that they did touch the board. (See 17) The sophomore also always tells the truth. Therefore, the person in recording #4, a sophomore, touched the whiteboard.