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In The Dark Knight, Batman removes a section a brick wall that contains a bullet. He takes it back to run some ballistics tests.

What are the reasons for the series of tests run here? Is the bullet so fragile that it can't be removed? Could it be contaminated if removed? Or has it already been shattered?

I think the ultimate goal is to recreate a fingerprint and identify who loaded and fired the gun. But shouldn't any fingerprint be on the case/shell which would either be in the gun or discarded on the floor -- and not on the actual bullet in the wall?

Removes section of wall with bullet hole

Fires bullets into bricks

Compares bullet holes

Analysis of bullet hole

Reconstruct bullet

Recreating the bullet with finger print

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Remember that fingerprints are made of skin oil. The high temperatures involved in the gunpowder explosion required to fire the bullet, combined with the high heat caused by impact on the other end, should have either burned off the oil or at least caused it to flow out of place, making the print useless. This is just another example of Hollywood being silly when it comes to forensics. (Warning: TVTropes link.) –  Mason Wheeler Jul 25 '12 at 14:31

3 Answers 3

up vote 10 down vote accepted

Here is a diagram of the parts of a typical bullet.

enter image description here

You can see that there is definitely a possibility of a person putting their fingerprints onto the actual bullet versus the bullet casing (depending on the size of the actual bullet). But, it comes down to a matter of likelihood. How many people handle the bullet itself versus the longer casing when loading their weapon?

There is also the fact issue of just how much of the bullet the print covers - more than is actually exposed in a typical bullet. So, this is either an exaggerated contrivance OR it could be that The Joker/a henchman assembled/inserted the bullet himself, deliberately planting a fingerprint on it for Batman to find and track down.

In most movies, I would go with the former, but with the elaborateness of The Joker's plots, the latter option is definitely plausible.

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Also, take a look at a bullet that punctured concrete. It would be smashed into a tiny round disc –  Denim Vallorosi Jul 25 '12 at 17:44
I have a lot of experience with firearms, and can definitely attest to the fact that loading a handgun magazine often is done by pressing the front of the cartridge back into the mag, thus leaving a fingerprint on its front (in this case, the bullet itself) –  SSumner Jul 26 '12 at 2:47

The goal of gathering physical evidence as a detective is to have the best possible chance of understanding what happened at a particular crime scene. In this instance, Batman gathers the entire chunk of wall because he believes it will be the best chance to acquire information from the bullet embedded in the wall.

Ballistic Technology Advances

Despite what you may have heard, it IS possible for modern science to get fingerprints from fired bullets. An article in the Guardian in 2008 [formerly published in the Journal of Forensic Sciences] discusses the technology required to get fingerprints from bullets that were previously unable to be acquired.

Scientists have developed a technique for retrieving fingerprints from bullet casings and bomb fragments after they have been fired or detonated. The new method, which relies on subtle corrosion of metal surfaces is already being applied for the first time anywhere in the world by two British police forces.

The patterns of corrosion remain even after the surface has been cleaned, heated to 600C or even painted over. This means that traces of fingerprints stay on the metal long after the residue from a person's finger has gone. The Guardian, United Kingdom, June, 2008 - Fingerprints recovered from fired bullet casings

Granted it is a recent development but if we give Batman the benefit of the doubt for the use of bleeding-edge technology, we should assume he would be able to do this too.

Here is an example of how a print might be placed on the fired round, not just on the case. Note the placement of the fingers:

Loading a magazine clip

He [Dr. James Bond] has published details of the technique in the latest issue of the Journal of Forensic Sciences. In his paper he demonstrates that it is possible to recover fingerprints from a bullet casing ejected when a pistol is fired. "As you are pushing the magazine in you are actually putting a thumb print on the bullet," said Bond. "That's the person you want. That's the guy who loaded the gun."

Forensic Ballistics

Forensic ballistics involves analysis of bullets and bullet impacts to determine information of use to a court or other part of a legal system. Separately from ballistics information, firearm and tool mark examinations ("ballistic fingerprinting") involve analysing firearm, ammunition, and tool mark evidence in order to establish whether a certain firearm or tool was used in the commission of a crime. We don't know if he gathered any casings (or whether any were left behind) from the scene either.

Since we know caseless ammunition exists, Batman may have simply decided it was easier to take everything ensuring any fragments, because bullets sometimes shatter and are usually deformed once they hit something, are going to be close together, giving him the best chance of acquiring, in this case, a fingerprint.

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And here I was thinking Q would have figured out how to do this. –  Pureferret Sep 19 '12 at 22:50

Is the bullet fragile that it can't be removed? Could it be contaminated if removed? Or has it already been shattered?

There's so many different situations that could've happened, it may or may not have shattered, but Bruce takes the precaution in case it could not be removed and preserved whole.

But shouldn't any fingerprint be on the case/shell which would either be in the gun or discarded on the floor-- and not on the actual bullet in the wall?

Not necessarily, have a look at: http://www.youtube.com/watch?v=5GIiQPSSoCs you can see that the bullet part of the round is handled and depending on how it is loaded could likely be the part that is pushed into the magazine.

Also, while the firing pin leaves its own "fingerprint" on the percussion cap of the shell, the rifling (the spiral inside the barrel that spins the bullet for stability) can also leave identifying marks.

ultimate goal is to recreate a fingerprint and identify who loaded and fired the gun

The ultimate goal as a detective, would be to gather as much evidence from a crime scene as possible (e.g. calibre, particular manufacturer, rifling marks, a fingerprint, DNA etc.), not with the aim in mind for something specific as a fingerprint.

Bruce preserves a part of the crime scene and transports it to his lab to get as much of that data as possible to have the maximum chance to create leads.

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