According to news sources, Manchester (UK) Police "could have uncovered what could be Britain's first 3D gun factory" (http://news.sky.com/story/1159349/police-find-first-3d-gun-printing-factory)
The two pictures below show the alleged gun parts - a magazine and a trigger. The only problem? The "magazine" looks like a Makerbot spool holder (like this, this, this, or this - there are a bunch more) and the "trigger" looks like the tension arm for the extruder upgrade (like this, this, or this official one from Makerbot and their blog post with a perfectly matching part).
In fact, the printer that is sitting less than a meter from me as I type this have similar parts installed on it -- and has been for many months.
Now, criminals are clever at hiding contraband in ordinary everyday things - but it seems like an unlikely situation in this case.
You can read more at the Greater Manchester Police website.