Dirk Gently
Batman would win, because he would have prepared the old man’s mansion with spy surveillance gadgets before the crime was even committed. He’s always prepared, except for that one villain whose superpower was to make random unpredictable shitty stuff happen to her enemies.
I’ll assume you mean 80s Batman, then. Not as ridiculously high-tech as his contemporary counterpart, and much less of a jackass; he was actually sometimes daunted at being in the JLA, otherwise composed of demigods and super-scientists.
That would explain Jason Todd being killed by the Joker, Babs Gordon being crippled and molested by the Joker, Ra’s Al Ghul stealing all his goodies to use on Kal, Di, & Co., & the 7,000 murders per week in Gotham.
No Arkady Renko?
I’m sure he’d soon see who the villain was!
Sherlock Holmes could claim he solved the case if physical evidence was involved, because anyone else who suceeded would be using his methods.
CSI could spot who’d fired a gun recently (paraffin test).
Goren and Eames (Criminal Intent) would spot any obsessive or cunning murderer.
**
Columbo** would only be able to find a murderer with a massive ego (though he would wear them down eventually).
It would be funny to have a final scene where **Nero Wolfe and Poirot **both try to give the assembled multitudes their analysis of the case.
It occurs to me that several of the detectives mentioned–I’m thinking Batman (assuming it’s the Silver Age version), the Jeffersons, the Charles, the Hardy Boys, Bobby Goren, & Nancy Drew–will decline to compete with Sherlock Holmes, whom they would consider the first and greatest of their number. At most, they’d all offer their services as his Irregulars. Hell, I would.
Ellery Queen was mentioned in passing, but deserves better. He would appear to be asleep the entire time or looking anywhere but the library. Then he would announce to thin air that he knew and ask the thin air to solve it too.
How about Brisco County Jr. (I think mentioned above)? Or Jeeves and Wooster who would show up if there was a party.
I seem to recall a biography of Jeeves (not written by Wodehouse), in one chapter of which Jeeves solves a mystery involving a jewelry theft–and showing up 3 famous detectives who are obvious parodies of Holmes, Poirot, and somebody else I forget.
A wonderful OP. As stated, the problem seems to belong to either Poirot or Roderick Alleyn, both of whom have seen similar plots. If it is a locked room mystery, then, as mentioned upthread, Carter Dickson’s Fell or Merrivale would fit.
In addition could I submit Inspector Ganesh Ghote, of the Bombay CID, who could just happen to be visiting relatives in the vicinity (works for both UK and USA.) He sticks to the book, disarms by his seeming incompetence, but his persistence and a bit of insight win in the end.
What, no Adrian Monk?
I’d say Lawrence Block’s Bernie Rhodenbarr character, but that would have to assume that he happened to be burgling the house on the same night the murder was committed, thus forcing him to solve the murder to clear his own name.
I would normally go with Wolfe and Archie, but this was just brilliant, so I’m voting with Chronos.
Holmes would team up with the scientists (CSI, etc.) immediately, because, at heart, Holmes is extremely logical, methodical, and scientific. He would instantly recognize the potential in the technology the 21st century detectives could bring to the table.
They’d solve the crime in about 15 minutes, while the rest of the detectives were mucking around with interviews and motives.
Gil Grissom and Sherlock Holmes would be instant friends, and Watson would be jealous. 
Mister Rik said:
No, first it would be difficult to get Monk there in the first place. He’d either have to fly (no no no) or drive (how far from San Francisco is it?). Then, he’d be delayed by cleaning his room, arguing with housekeeping for not using enough starch in his sheets, and tripping over inconveniently placed objects. Plus, he’d freak out when he seens Scooby in the room, never mind Shaggy. He’d be catatonic after accidentally eating a Scooby Snack.
It would be Sargeant Lewis, of course, but Inspector Morse would get the credit.
Actually, nowadays Morse is dead and Lewis is the top detective with his own assistant.
Mmmm, probably a 60s Batman. That’s when I was reading superhero comics, in the 60s. I watched 1988’s movie Batman (with Michael Keaton), and the sequels to that. I’ve seen the Batman movie after that, but not The Dark Knight.
So, pick a Batman, any Batman. I don’t know most of them, and at this stage of my life, I really don’t want to try to start catching up on all of them.
He could do it over the phone, or by webcam. He once solved a French murder he read about in the newspaper, and called to tell the French police.
You forget that Batman does in fact have the greatest power of all superheros: An ever expanding bank account.
If you come up with a tough situation that can’t be solved, send it to R&D!
