I was idly watching a bit of CSI: Vegas last night, and it got me thinking about forensics in 40k. Now I have absolutely no science background at all, but I was wondering how the field might operate in 40k.

In particular, last night's episode was very ballistics-heavy. In the real world, guns are matched to crimes via the study of the bullets at the scene. These are then linked to individual guns, which are linked to individual criminals.

In 40k, one of the most ubiquitous weapons is the laspistol. If the Arbites (or local Magistratum/Enforcers) find a dead body, and the victim has been killed by lasfire, how do they go about matching the crime scene to a particular weapon?

Does each lasgun produce a particular "signature?" One would imagine that the injuries inflicted by a Civitas-pattern laspistol are less catastrophic than the injuries inflicted by a hellpistol, but would these differences be sufficient to link the injuries to a particular weapon?

Would the colour of any lasgun's beam make any difference? Would a red beam produce different burn patterns to a green beam for example? Could the colour of a lasgun's beam be determined from the wounds? If so, then you could potentially match wounds to guns by that route...but I have no idea if that's scientifically feasible...

I am no scientist either. However, I would think that you could determine the relative power of the Las-weapon (as per your example, Civitas compared to Hellpistol) in question by the intensity of the burns. But I seriously doubt that you could do so with enough refinement to link it to a specific weapon.

As for the color of the beam, that is determined by the wavelength of the light emitted by the laser. I honestly don't know if there is a way to determine that from a las-weapon wound. If there is, I would guess it would be quite high-tech, and in 40K, quite rare and expensive. It would have to be something that could examine the damaged cells on a molecular, or perhaps even atomic, level. Generally speaking, the lower the wavelength the higher the power, and vice versa. Perhaps you could determine that by the amount, or type, of damage to certain cell structures. But I wouldn't bet on it.

I expect that plasma and melta weapons would be even harder to trace, as they tend to vaporize the evidence.

Flamers, on the other hand, might actually be easier, since they use a sticky fuel that could be much more easily identified and traced.

Just my two cents.

Yeah, that's kind of what I thought too, Sister Cat. It would actually tend to make laspistols/lasguns excellent assassin's weapons, because it would be so difficult to link victims to weapons. Also they're incredibly common weapons, so many people are packing them.

Like you say, plasma pistols and flamers may destroy the evidence, but they're rarer (plasma pistols especially) than laspistols, so if there was a killing with a plasma pistol, the enforcers need only look for someone rich enough to afford one - this may not be too hard in the grimier parts of an underhive!

Lightbringer said:

Very true. Kind of sheds a new light on the Long Las, yes? Or even a Laspistol with a Hot-Shot Charge pack at point-blank range ... nasty.

Sister Cat said:

Untraceable... for a rookie enforcer squad maybe. But if it's a crime that matters, then you'll definitly want to include a diviner on your verispex team. Not even a laser can hide from the all seeing eyes of the Emperor as viewed through His Tarot. CSI's mentioned in the subject, yet somehow the mystic and magical elements of crime solving have been forgotten... odd ;-)

One of the first and most important lessons in Assassination 101 is "when the job is done, get rid of the gun ASAP"...

As laserlight (photons) are linked to specific frequencies/energies (and that is seperate from intensity/power), I'd imagine that type of weapon (and possibly even whether it was fire on single/semi) could well be seen in the blast-impacts and how badly/not affected the target material was.

That is: empiricism. A hellpistol will do different things to a body than a laspistol, especially if one bores straight through and one doesn't. It'd be a complicated thing (depending angles, what bits of armour and clothing are in the way), but at it's heart its still basically materials physics. Some additional bits on how they interact and react with certain materials, and particular effects on biology, but with las weapons I imagine it'd be possible to narrow down some of the details, possibly all.

Indeed, depending on accuracy of measurements, it wouldn't surprise me to learn that individual weapons of the same class could be distinguished and 'finger-printed'. (Lens and chamber impurities could be correlated, even between weapons of the very same batch.)

By similar reasoning, of course, it's absolutely possible that differentiation between types might simply be unlikely or impossible, given equipment, time frame, feasibility or even simply the massive number of microstates and macrostates 'possible'. I.e. the variation might be too much and too coincidental to really permit sensible analysis. But, if you're (or your group are) non-scientists (or scientists who can accept the nonsense, magic and pseudoscience involved in, say, CSI: Ancient Terra), I strongly advise using the above paragraphs.

Plenty of opportunity. Frequency signatures, set-segments of spectrum fluctuation, vaporisation traces, scoring, angle-important effects on internal organs or bones and fleshy layers. Lots of possibility, and if you're scientific illiterates, then it's quite possible to make it really quite plausible, the trouble would be 'convincing' someone who has an idea about what you're talking about (or persuading them to fly with it).

It's possible in project-future reality, also possibly not. Some explanations make sense, but we'd really have to check (or do some mad exhaustive theorising, calculating and analogising), so best stick to 'magical science can do stuff without detail' for now. The (now far) above is what I'd use in that manner.

Notes in my games there are:

Arbiter and Tech priest crime scene investigators.

Darklight las weapons- Basically these use either the UV or IR spectrums

Neural extractors- A device large device with sharp probe inserted into the brains of the dead. If the brain is fresh enough the tech priests can often extract random memories.

Mechanical mind probe- A servitor and funky looking helmet. If you shave a subject, and put the helmet on him the servitor starts babbling the subject's thoughts. Often

Graver said:

I think it's heavily implied, seeing as CSI seem to mainly use magic (masked as science) to find the perps.

If this was Star Trek you could convict someone by the burn signiture of there weapon on the victim. Seeing as even individual weapons within a make will probably vary in intensity AND wavelength it's probably only good for working out the weapon type (with Imperial tech anyways) and they'll be better off with good ol fashioned police work and psykers.

Besides where as CSI is trying to prove some-one is guilty the Arbites can 'request' a suspect confesses.

I'd consider lasweapons pretty much untraceable with what most planetary law enforcements have at their hands (though different classes of weapon may be separated). When it gets to Arbites and AdMech, things may get a little more fuzzy and mostly depend on what ressources they want to be spent on a case.

Considering the shear volume of las weapons floating around, and the fact that all the las shots from the same type of gun would look the same, you would need to roll out the pyskers to figure it out.

Oh I don't know ... considering that this is Dark Heresy, we accept magic and pseudoscience every time we play. Hell, no-one's argued about the feasiblity of a laspistol in this thread, right? Given that, I don't think tracing las-weaponry foresically (Or by whatever nonsense-latin name the Imperium now calls it) is that far-fetched