Alice's body is found inside a locked room. She had been getting ready for the day, and had only just gotten out of the shower and had written a letter when she died. The police had to break the door down in order to enter. In the room they find the following:

  • A pen
  • A cup of tea, half drunk
  • Trash can, including a used teabag
  • Lipstick, open
  • Letter sealed in novelty envelope
  • A humidifier, still running when the police arrive
  • The broken chain from the door lock
  • The broken latch from the door lock

The police discover that Alice has been poisoned by Cyanide! Immediately, the tea is tested, but there is no poison in the tea. Forensics confirm that Alice consumed the poison in the room! But how?

Can you solve Alice's murder?


The murder method has nothing to do with her shower, or anything in the bathroom. She was killed by one of the items listed.


I suspect the cyanide was hidden

on the envelope, as it's common practice to seal it using your tongue.

  • $\begingroup$ +1 for quick solution! I will accept the answer once the mandatory waiting period expires $\endgroup$ – GridAlien Aug 13 '19 at 16:58
  • $\begingroup$ Or on the stamp. $\endgroup$ – Florian F Aug 14 '19 at 10:21
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    $\begingroup$ @GridAlien - Could have been in the lipstick, too, no? $\endgroup$ – Voldemort's Wrath Aug 14 '19 at 13:12
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    $\begingroup$ Seems like the murder has been watching too much Seinfeld... $\endgroup$ – Nuclear Hoagie Aug 14 '19 at 15:09

She was well-known among her friends for chewing on the end of her pen, especially while thinking about what to write. The murderer is obviously a close friend of hers, and the poison was applied only on the very tip of her pen, impossible for the police to find.


It's also possible that:

The cyanide was in the lipstick. If it is open, the riddle implies that could have been used. Lipstick can be put on anywhere, not just in the bathroom.

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    $\begingroup$ Was trying to imply that this was not possible, as she had just gotten out of the shower, hadn't yet reached that stage of getting ready. +1 for thinking of it $\endgroup$ – GridAlien Aug 13 '19 at 17:24
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    $\begingroup$ If the lipstick is open, it suggests it was being used. $\endgroup$ – Florian F Aug 14 '19 at 10:12
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    $\begingroup$ @GridAlien Writing a letter is usually not in the middle of peoples' morning routines of getting ready either. Seems weird for doing paperwork to be in-between getting out of the shower and putting on makeup. $\endgroup$ – Southpaw Hare Aug 14 '19 at 16:56
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    $\begingroup$ @SouthpawHare For that reason and the others mentioned above, I don't think this is a good puzzle. $\endgroup$ – user91988 Aug 14 '19 at 19:41
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    $\begingroup$ I thought this as well. The combination of the envelope being novelty and sealed and the lipstick being open led me to conclude it wasn't on the envelope, rather it was on the lipstick - potentially she was sealing the novelty letter with a kiss on the envelope and that's when it all went down. $\endgroup$ – Ecchi-Alex Aug 15 '19 at 8:30

Another possibility could be

I'm no chem expert but a quick google search says Cyanide could exist in the air in the form of Hydrogen Cyanide, which could've been added in this case through the humidifier.


Since the humidifier was still running when the room was opened, it would also kill anyone who enters the room too, or at least cause some adverse effects.

Edit :

If the killer was a good engineer he/she could tamper the humidifier to only emit poisonous Hydrogen Cyanide for a certain amount of time, this would ensure that anyone who enters the room later on will not be affected as severely. Still keeping in mind that would leave traces of the poison in the air. But most of it could leave through any openings in the door.

Edit 2: Nothing to see here, Thanks to @Loong, we know this edit to be pointless.

My friend informs me, The International Standard Atmosphere states the density of air is 1.225 kg/m³ at sea level and 15° C. Hydrogen Cyanide is extremely dense at 687 kg/m³, it would not disperse in the air and immediately fall low to the ground. Rendering the poison ineffective. So there's that theory down the drain.

  • $\begingroup$ But the forensics confirmed that Alice rot13(pbafhzrq, abg vaunyrq) plus they also confirmed that rot13(gurer jnfa'g n genpr bs plnavqr va gur grn). Also, based on the circumstances rot13(Nyvpr jbhyq or yrff yvxryl gb qvr ol gur uhzvqvsvre guna gur vairfgvtngvba grnz qhr gb znal ernfbaf). Oh and rot13(gur vairfgvtngvba grnz zhfg'ir fcrag zber gvzr vafvqr gur ebbz guna Nyvpr) $\endgroup$ – Adam Aug 13 '19 at 18:48
  • $\begingroup$ pbafhzrq, abg vaunyrq that'd be a good point if rot13(gurer'f n qvfgvapgvba orgjrra gur gjb), rot13(Jul jbhyq gurer or hayrff Ulqebtra Plnavqr pna ernpg jvgu gur grn ryrzragf?) the other two arguments seem to counter each other, I'm not sure what to say to that, except I did add that bit in my answer. $\endgroup$ – Abbas Aug 13 '19 at 19:04
  • $\begingroup$ Well, if cyanide couldn't dissolve in the tea then the forensics team wouldn't have checked it! And the reason why the cyanide must've ended up in the tea in this scenario is because rot13(gur uhzvqvsvre pyrneyl pvephyngrq vg'f incbhe guebhtubhg gur jubyr ebbz). Also, since she showered rot13(genprf bs plnavqr fubhyq or sbhaq va gur jngre naq gurer vf n uvtu cbffvovyvgl gung Nyvpr qenax sebz gur grn juvyfg fgvyy jrg fb gur qvffbyirq plnavqr pbhyq znxr vgf jnl vagb gur grn sebz n qebc). Although interestingly enough she could've consumed it using the same logic! rot13(jngre qebc va zbhgu) ;) $\endgroup$ – Adam Aug 13 '19 at 19:31
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    $\begingroup$ However these are all shots in the dark, I feel we need a real chemist to accredit or discredit the theory. $\endgroup$ – Abbas Aug 13 '19 at 20:19
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    $\begingroup$ The density mentioned in your "Edit 2" is for liquid HCN. At typical room temperatures, however, HCN has a vapour pressure of about 800–1000 hPa; i.e. HCN would evaporate quickly and not form a liquid. $\endgroup$ – user2503 Aug 14 '19 at 6:36

It's not reasonable to be running a humidifier during or after a shower, as the shower itself will accomplish that function. We may thus find it likely that the humidifier was interfered with. If it was an ultrasonic humidifier, it would form a mist from the liquid in the reservoir. If that liquid were spiked with a cyanide salt such as potassium cyanide, the victim would consume it by inhalation.

Edit: this answer does not account for the locked door, so I consider this to not be a great solution. (It would be cheating to add "and the attacker had a key", since that's against the spirit of the question design: the door was not opened from the outside.)

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    $\begingroup$ @Rubio I found that the answer you mention did not address any of my points. However, I will add a clarification (regarding the exact compound) to distinguish further. See this reference which describes that this delivery mechanism is plausible, regardless of what the other answer claimed: cdc.gov/niosh/ershdb/emergencyresponsecard_29750037.html $\endgroup$ – piojo Aug 14 '19 at 5:33
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    $\begingroup$ Also, the ROT13 thing is driving me nuts, so I can't argue this any further. If my points as written are not convincing, I nonetheless have to let them stand. $\endgroup$ – piojo Aug 14 '19 at 9:21
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    $\begingroup$ @Adam To me it seems like that link supports me rather than ruling out the explanation. You are correct about the locked door, so this answer is not right. It would feel like cheating to say "and the attacker had the key", so I'll note the flaw in my answer. $\endgroup$ – piojo Aug 14 '19 at 10:11
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    $\begingroup$ @piojo Me too. The worst is comments that start in english and end in gibberish. Please stackoverflow, add spoiler tags that work in comments! $\endgroup$ – Florian F Aug 14 '19 at 10:19
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    $\begingroup$ Sorry, I forgot to say that the symptoms are a huge problem with this delivery method. There is a clear difference between the different exposures so the investigation wouldn't mix them up. However, the main flaw is actually how death can occur in minutes - it is unreasonable for the humidifier to be running during her shower. Then it must've been switched on while she was writing the letter. But if this is the case then it doesn't make sense why the humidifier was still running on discovery as the first thing I would do when feeling ill is turn it off! Keep in mind she finished the letter $\endgroup$ – Adam Aug 14 '19 at 10:26

Another possible answer is:

The poison was planted inside the shower-head. Enough of that stuff gets on you in a shower and you might absorb it through your skin. Or some people might take a gulp of water while in the shower.

You might also want to check:

Any oral hygiene products in the bathroom - toothpaste, toothbrush, mouthwash, dental floss, etc. Many people use those during or after a shower. Generally you spit them out, but you might ingest enough from normal dental care to be lethal if there's cyanide in there. (Also, minty flavor would be a good way to mask the taste of the poison.)

  • $\begingroup$ rot13(V guvax fur'q qvr vzzrqvngryl nsgre pbafhzvat gur cbvfba, plnavqr jbexf irel snfg, fur jbhyqa'g unir unq gur gvzr gb jevgr n yrggre be qb nalguvat.) $\endgroup$ – Abbas Aug 14 '19 at 13:12
  • $\begingroup$ Oh, whoops, I missed the hidden text in the hint that negates this answer - or was that added afterwards? $\endgroup$ – Darrel Hoffman Aug 14 '19 at 14:30

I propose that the following is what happened:

Alice lives in a small apartment by herself in a city where either the weather or climate is dry. She relocated here recently. She drinks tea in the morning to try to wake herself up better, but perhaps that doesn't suffice. So instead, she goes to take a shower to help wake her body up, but the water is drying to her skin. Perhaps she realizes her lips are dry, begins putting on lipstick, and then remembers that she has a new humidifier she could use. So she puts the humidifier on to help regain some moisture in her skin. This humidifier happens to have been gifted to Alice by the murderer, as a house-warming present. The humidifier contains some non-volatile compound containing cyanide, such as a cyanide salt, unbeknownst to Alice. When the humidifier is turned on, the water in the machine heats up and reacts with the salt, creating hydrogen cyanide gas. Any steam from the shower would have accelerated the reaction, but it still takes a while for the gas to reach levels of toxicity. After turning on the humidifier, Alice sits down and writes a thank-you card to the person who gifted the humidifier. She seals the envelope and, well, the effects of the gas have taken their lethal effects by now.

  • $\begingroup$ You should see these answers 1 and 2 which have both examined the possibility of this. There are some big issues that you have to address $\endgroup$ – Adam Aug 15 '19 at 10:33

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