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There's this fun Japanese crime mystery show called Galileo where a physics prof solves similar 'classic' crime story tropes.

My favorite 'modern' solution to the locked room was, spoilers!, that the door with a large handle to the room appeared locked at the time of the crime because the murderer was using a small hologram to make it appear locked from afar.

In fact, there's a huge literature genre in Japanese fiction: Honkaku, reanimated in the 90s as Shin-Honkaku. Do yourself a pleasure and go read Edogawa Rampo.

> The murderer is still inside the room, very well hidden. Say, inside the sofa where the stuffing should be, waiting very quietly until the investigation is over so they can leave.

Not a murder, but this is essentially the resolution of a Spike Lee movie. (no name - no spoiler)

When I think couches with people inside I cant get Frank from Always Sunny climbing naked out of a couch out of my mind.

Ummm, I think it's probably spoiled from context and connection alone, right?

From the systems security mindset - the doors and the windows are only the most obvious ways to enter the room, not the only ones. If you secure them very well, then the walls, floor and the ceiling become the best points of entry. (Chimneys are kind of obvious)

Maybe the soon-to-be murderer just lifted the ceiling with a crane, killed the victim (thus becoming the murderer) and put the ceiling back in its place?

- The murderer completely seals the room from the outside so that no oxygen can go in, and waits for the victim to suffocate.

- Similar but just prevents the victim coming out long enough for them to die of thirst.

- Murderer comes in with heavy machinery and breaks down the whole building except for the locked room, then lifts the locked room and drops it off a cliff.

Or throw some Havana style mystery in the mix.

https://www.bbc.com/news/world-58396698

> - The murderer was not in the room when the murder happened. Poison or a trap of some sort. (Kinda boring.)

Slow-acting poison seems easily the most obvious way to do it. I would hope every locked-room investigation quickly rules this out.

> - The murderer was in the room when the murder happened, but locked the door behind themselves. (This one doesn't really work because the door is presumably of a kind that can't be locked behind you, or else no one would be surprised. Good to double-check, though, that you're sure the door couldn't have been locked behind someone leaving.)

The clever trick might be in how the murderer managed to lock the door behind them. Using a magnet to shift the bolt, perhaps? (I'm sure this option must have been explored very early on in the locked-room genre.)

one of my favorites:

- The room doesn't even need to be completely locked, people just need to think that it was

In many TV shows it ends up being the person that first gets into the room (supposedly after the person is already dead, but not in reality) that does the killing. I.e. police, family member, medical staff, etc.

> Are the windows locked? Otherwise it's a rock climber who can climb the side of the building. Some buildings are not that difficult to climb for a good climber.

I'd probably rather just do a retrievable abseil to ground level to minimise risk. However I feel like we're subverting the meaning of "locked room" if it has unlocked egress points. ie ground floor window, or fire escape outside high window etc.

Depending on the room, the murderer could have blocked the chimney/windows from fresh air, letting the victim to suffocate to death.

Carpenter here, how would you trim the door on the inside of you pulled it out?

That's gonna be pretty obvious.

Also: it wasn't a murder, the apparent foul play is illusory.

Bonus points for any combination of the possibilities.