http://www.cbsnews.com/news/europes-small-arms-plague/ (1998)
https://www.washingtonpost.com/world/europe/getting-a-gun-le...
And many many others, unfortunately. It's a very nasty thing and it will take an extraordinary effort to put this genie back into the bottle.
Open borders has been a blessing in many ways but at the same time it has caused a whole bunch of un-intended side effects and this one and cross border heavy crime are two of the not so nice ones, to put it very mildly. We now have actual gangs with heavy arms in Amsterdam which was a fairly peaceful city not all that long ago.