1. The sixth-floor door and the lobby door each have a badge reader. Room 612 has its own reader on the same floor. The sixth-floor reader logs a badge going in and the next swipe as going out.
2. The building has one working elevator. Between the lobby and the sixth floor, the ride, including the wait, takes at least 3 minutes. The stairwell is locked.
3. A badge can be used only by its owner, or by someone who borrowed it. Exactly one swipe in the log was made by someone other than the badge’s owner.
4. The laptop was on its desk at 6:00 p.m. At 6:16 p.m. its tracking tag was read at the lobby doors as it left the building.
5. The only entry on the Room 612 door between 6:05 and 6:14 is the one marked below. Whoever made that swipe took the laptop.
The badge log:
Priya: lobby 6:00, sixth floor 6:04, sixth floor 6:15, lobby 6:19
Marcus: lobby 6:10, Room 612 at 6:11, lobby 6:25
Dana: lobby 6:12, sixth floor 6:19, sixth floor 6:26, lobby 6:30
Tom: lobby 5:57, sixth floor 6:01, sixth floor 6:12, lobby 6:15
Which timestamp is impossible, and who took the laptop?
💡 Hint
Test every consecutive pair of swipes against the 3-minute travel rule to find the impossible one. Then compare who was upstairs at that moment with who could reach the lobby by 6:16.
Reveal answer
Tom took the laptop. Marcus’s Room 612 swipe at 6:11 is the impossible timestamp, and Tom was the only person who was on the sixth floor at 6:11 and could reach the lobby by 6:16.
Step-by-step solution
- Check every consecutive pair against the 3-minute rule between the lobby and the sixth floor. Priya’s lobby 6:00 to floor 6:04 gives 4 minutes. Dana’s lobby 6:12 to floor 6:19 gives 7 minutes. Tom’s lobby 5:57 to floor 6:01 gives 4 minutes. Marcus is the problem: lobby 6:10, then Room 612 at 6:11, one minute apart. That is impossible.
- Marcus also has no sixth-floor swipe, so he never went up. His badge was used at 6:11 by someone else, and by fact 5 that person took the laptop. Marcus was in the lobby and is cleared.
- The thief was therefore already on the sixth floor at 6:11. Read each person’s time on the floor from their two sixth-floor swipes. Priya was up there from 6:04 to 6:15, Tom from 6:01 to 6:12 and Dana only from 6:19 to 6:26. Dana arrived after the laptop was gone, so she is cleared. Priya and Tom remain.
- Now use the tag. It was read at the lobby doors at 6:16, so the thief must have left the sixth floor early enough for a ride of at least 3 minutes, which means no later than 6:13. Priya swiped out of the sixth floor at 6:15, so the earliest she could reach the lobby is 6:18. She is cleared.
- Tom swiped out of the sixth floor at 6:12 and reached the lobby at 6:15, which fits the 6:16 tag reading perfectly. Tom borrowed Marcus’s badge at 6:11, took the laptop and carried it out. Testing every possible impossible swipe and every possible thief confirms that no other world fits.
Why it fools people
The log hands you a ready-made suspect in Marcus, and that is exactly why it works as a trap. His name is attached to the one event that matters. The detective’s move is to ask whether the record could be true, not just what it says. Once one swipe is shown to be impossible, the entry that seemed to convict Marcus clears him instead. Test a record against physical limits before you build a story on it.
Did you get it?
About This Puzzle
On the sixth floor of an old waterfront building in Seattle, a small design studio keeps a prototype laptop in Room 612, locked behind a door that opens only to a badge. One rainy evening it disappeared. The office manager pulled the badge log for the four people in the building and found something odd right away: one entry is not physically possible. This case rewards patience with a clock.
How to Think About It
Treat the log as a set of moves on a map. For each badge, list the places in order and ask whether the person had enough time to get from one to the next. Mark any move that breaks the rule about travel. Once you find a swipe that cannot belong to its owner, ask a new question: who was actually close enough to make it? Then use the second piece of timing, the tag at the lobby doors, to separate the people who could have been there.
Common Traps
The obvious trap is to accuse the person whose name sits on the Room 612 entry. A name on a log is a claim, not proof, and here the log itself shows the claim cannot be right. Another is to stop once the field is down to two people. Two suspects is not an answer, and the last fact on the page exists to break the tie.
Where This Puzzle Comes From
Puzzles built on timetables and alibis are a classic strand of detective fiction. In the Golden Age “fair play” tradition, the reader could follow every deduction, and a train schedule was a favorite tool. Here a badge log replaces the timetable. This case is original.
Try This Variation
Suppose the lobby tag reading is missing entirely, because the reader at the front doors was unplugged that evening. Everything else in the case stays the same. Whom can you name as the thief?
Show the answer to the variation
Nobody, but you can narrow it to two. Marcus’s swipe is still impossible, and Dana is still cleared, since she arrived after 6:11. But Priya and Tom were both on the sixth floor at 6:11, so either could have used Marcus’s badge. The 6:16 reading is the clue that separates them.