For 80 years, Batman has been the top dog of superheroes, even convincing fans he could potentially exist in the real world. But just how long would it take the Gotham Police Department to figure out the 'Dark Knight' is really billionaire playboy Bruce Wayne? Both comic book scribes and comic book readers alike have asked this question, but with Batman’s mythology existing in both fantasy and science fiction, it is impossible to come up with a definitive conclusion. His cave full of “wonderful toys,” super computers, and military grade urban assault vehicles would give him the element of surprise at first... but not even Batman could escape the law forever.
While city police have apprehended several RLSH, or “Real Life Super Heroes” in the past--most notably the Seattle PD in their arrest of Phoenix Jones--Batman would be too big a fish for local or even state police to handle on their own. Phoenix Jones, whose real name is Ben Fodor, unmasked amid a crowd of reporters outside a courtroom back in 2011, after police arrested him on four counts of assault while breaking up a nightclub fight. In his normal life Fodor is a skilled mixed martial artist--not quite at the god-tier level of Batman, but the RLSH has stopped both muggings and assaults while in his Phoenix Jones persona. He has even been stabbed and shot at, but avoided serious injury thanks to ballistic armor built into his “super suit.”
Phoenix Jones may be the closest thing the world has to a costumed crime-fighter, but it didn’t take the Seattle PD very long to arrest him, especially after a video of Fodor macing a purse-swinging woman was posted online. A loud, havoc-causing vigilante with Batman’s vast resources on the other hand would quickly land on the FBI’s most-wanted list. Throughout his career a CVS receipt-sized list of major Batman felonies has accrued, including copious amounts of assault, unlawful imprisonment, tampering with evidence, and pretty much every rule of the road in regards to the Batmobile. After a few nights of Batman pancaking Don Falcone’s fleet of unmarked, black escalades with his car the city, state, and federal law enforcement agencies would be on him faster than Robin could say “holy incarceration, Batman!”
What methods would law enforcement employ to unmask Batman? In the "Ask Science Fiction" section of Reddit, the question's received responses ranging from informative to hilarious. The top answer, by Redditer "totalprocrastination" suggests it wouldn’t take long at all, citing the 1990 Legends of the Dark Knight story "Prey." Taking place about 18 months into Bruce's career as a costumed crime-fighter, the psychologist supervillain Hugo Strange figured out Batman’s identity by examining the equipment he leaves behind at crime scenes, the types of criminals he targets, first-hand accounts of his physical appearance, and cross-referencing the data with police records.
The results suggest that Batman would have to be a man with access to extreme wealth, in his physical prime, and have a personal grudge against the criminal underworld of Gotham. All things considered, it would narrow down the list of suspects considerably. Forbes 500 level bank account? Check. Free time to work out and train in multiple forms of combat? Check. Access to vaguely Batman-themed military weapons? Check. Parents murdered in a senseless crime? Bruce Wayne is Batman!
Another commenter, "periphery72271," claimed it would take exactly one month after showing up on the radar of federal authorities for Batman to be unmasked. His theory involves “several Blackhawks and Little Birds from the BATF and FBI” orbiting on surveillance shifts scanning for the Batmobile’s unique turbine-driven heat signature. Once located, the Redditer claims a predator drone would be sent out to film the Batmobile through infrared enhanced video. Over the next several days, special operations elements from the Department of Justice would mount cameras and other high-tech sensors around known paths Batman has taken during his nights out fighting crime. Even with all the secret tunnels and shortcuts the Batmobile takes throughout Gotham, a grid would be established marking patterns in the Dark Knight's movement and before long many of the Batmobile’s hidden passages would be uncovered.
Eventually, with enough video capturing Batman’s vehicle, armor, and extensive weaponry along with any physical evidence Batman leaves behind after his skirmishes, the FBI would start looking into purchase orders for items fitting the descriptions of Batman’s technology. The DoJ would disassemble every piece of Batman’s arsenal and, like a jigsaw puzzle, piece it all back together with the irregularities in Wayne Enterprise's R&D budget. Likely, the feds wouldn’t come after Batman directly, but would arrest Bruce Wayne in his own office to avoid a direct battle with the Dark Knight.
If real life Batman were clever, which he most definitely would be, he would limit his use of the Batmobile as much as possible. Predator drones aside, Batman would run the risk of getting stuck on a Gotham turnpike in rush hour every time he peeled out of the Batcave. And being caught in traffic is a good way of being caught by the five-0. Likely, Batman would keep his armored Lamborghini-tank somewhere hidden and only use it as a means of quick escape after beating the holy hell out of known criminals rather than a shock-and-awe weapon of mass destruction like in the comics.
Even if he were stealthy in his use of the Batmobile, Batman would need to be careful with what he left behind at crime scenes. Something as simple as a used batarang lodged into the shoulder of a mafia enforcer would give the FBI evidence to examine with an electron microscope. All it would take is for one of the countless private contractors tasked with assembling the many intricate physical parts of Batman’s war on crime--his million dollar computer, his armor, his weapons--to wise up to what they’re really building once the feds started asking around.
And should Bruce leave any of his own blood behind after a fight, that would only further speed up the timetable on his inevitable capture. And considering Batman bleeds a lot in the comics, it is unlikely he would have enough time to bleach down a whole crime scene before fleeing the police. Essentially, every night out would be a night closer to Batman’s identity being discovered. Much like your average serial killer, he could only remain active for so long before getting caught.
If Batman spaced his nights out to only once or twice a month and kept his activity sporadic, it would take longer for the police to develop a pattern. But Batman doesn’t wait around. Crime doesn’t take a night off and neither does the Caped Crusader. If Batman were to go out every night like he does in the comics he wouldn’t make it through year one of his mission before law enforcement discovered his secret identity. But the real question isn’t how long it would take the police to discover Bruce Wayne is behind the cowl; it’s whether or not law enforcement would want to capture him at all.
In the beginning of The Dark Knight, the Major Crimes Unit tasked with apprehending Batman jokingly lists Sasquatch and Elvis as potential suspects because they have no interest in catching him. He does a lot of the heavy lifting for the GCPD and on his own dime to boot. If his only major crime is making their lives easier, its easy to understand why the beloved Commissioner Jim Gordon looks the other way when Batman commits a felony or three every night he steps out in his cape and cowl.
As long as real life Batman doesn’t kill, which he doesn’t, and he keeps the property damage to a minimum, then allowing a one-percenter vigilante to clean up the murder capital of America might be a good way to save tax payers some money. And being able to blackmail a billionaire superhero with knowledge of his nightly escapades would be an asset Uncle Sam would likely exploit and milk to its fullest, which is exactly what Amanda Waller already does in the comics. So even though Batman’s identity wouldn’t remain secret for very long, he could potentially remain active for many years as long as he keeps public opinion on his side and doesn’t piss off anyone in Washington.
But if real life Batman’s chin happens to be extra prominent--specifically Batfleck level prominent--then Facebook’s auto-tagging technology could “out” Batman the moment a picture of him leaked online, thus making every other aforementioned point entirely moot.