Elementary S02E01

Elementary S02E01 - Step Nine

This episode featured another product placement of Microsoft's Surface tablet, but was otherwise relatively computer free. Instead, the episode focused on 3D printing.
The murderer 3D printed a plastic gun, killed his wife with it, and resolved the plastic parts in acetone.

A Surface tablet showing a plastic gun.

3D printed guns were a huge topic in 2013 when Defense Distribute, a Texas based nonprofit, first fired their "Liberator", a fully 3D printed gun. Similar to the episode the plastic gun needs one metal piece: a nail, used as the firing pin. (The Liberator also includes another metal object because of regulation).

It is noteworthy that the first iteration of these guns wasn't 100% stable. According to the embedded video, one of the first prototypes exploded. This is something that happened to the murderer in the episode, too. Clearly, the episode writers got their idea from one of these videos or articles that came out in 2013.
Since 2013, 3D printed guns have evolved. I'm sure the design of the guns has been improved, but there is furthermore work on the right ammunition for these guns: http://www.wired.com/2014/11/atlas-314-3-d-printed-guns-bullets/

As mentioned above, the murderer decided to hide his gun by dissolving it in acetone. Conceptually that works: ABS (the plastic commonly used in 3D printing) dissolves in acetone.

However, I doubt that a huge piece of ABS (like the gun) would dissolve so rapidly. Also, it looks like the gun doesn't even fit into the jar:

Jar of Acetone and the 3D printed gun.

Given that the gun needs to withstand huge forces, it is unlikely that the right piece could be disassembled into smaller pieces...

Scientifically, this episode was well researched. There are some nits (like dissolving such a huge ABS block takes time), but it could work. Where this episode falls down, is common sense: nobody would hide a tiny nail by hammering it into the wall. Where would you hide the hammer? If you had already a toolbox, why not hide the nail there?
It's also unrealistic to assume that every 3D printer is tracked. In fact, some 3D printers are able to (mostly) print themselves (see all the options on reprap.org). There would be no trace of them anyway.

RepRap from Adrian Bowyer on Vimeo.