SOPOT, Bulgaria -- Shortly after sunset on March 21, 2015, the skies above Bulgaria's biggest, and last remaining state-owned, armaments factory filled with the crackle and fury normally associated with a battlefield.

The massive fire at the VMZ plant destroyed a large cache of weapons and ammunition and terrified residents of Sopot, central Bulgaria, and neighboring towns abutting the Balkan Mountains that stretch from Bulgaria's western border with Serbia to the Black Sea coast.

Emil Kabaivanov, the mayor of nearby Karlovo, described fire plumes up to 200 meters high: 'You could see things exploding in the air.'

Less than a month later, on April 14, there were more blasts and more damage at VMZ.

Two weeks after that, a major Bulgarian arms dealer, Emilian Gebrev, fell into a coma, the victim of a poisoning that he alleges some state investigators still attribute to a bad salad and 'other ridiculous claims.'

All three incidents were part of a string of unexplained explosions (and a poisoning) affecting Bulgaria's arms industry, beginning more than a decade ago and seemingly intensifying after Russia invaded and occupied Crimea in 2014 in the first phase of its expanding war to subdue Ukraine.

WATCH: A special RFE/RL investigation looks into allegations of Russian sabotage, cover-ups by Bulgarian authorities, and whether Bulgarian arms depots are still at risk as Russia's war in Ukraine enters a second year.

Copyright (c) 2018. RFE/RL, Inc. Republished with the permission of Radio Free Europe/Radio Liberty, Washington DC 20036