MOSCOW (Reuters) - Russian military investigators are now treating the Nov. 9 downing of a helicopter over Armenia as “wilful murder”, a more serious charge than the previous “death through negligence”, Interfax news agency reported on Monday, citing a source. A Russian Mi-24 helicopter was shot down over Armenia near the border with a region belonging to Azerbaijan, killing two crew members and injuring another, just few hours before a Moscow-brokered peace deal over Nagorno-Karabakh was reached. Heavy fighting between Azerbaijan, which has the political backing of Turkey, and ethnic Armenian forces over the mountainous region had been raging for six weeks at the time of the incident. Azerbaijan’s Foreign Ministry said Azeri forces shot down the helicopter by accident, expressing apologies to Moscow and a readiness to pay compensation. Interfax said on Monday, citing the source, that a case had initially been opened into a potential infringement of flying regulations that had resulted in deaths through negligence. The reported switch to a murder charge, which could lead to a sentence of life imprisonment for those held responsible, may complicate relations between Moscow and Azerbaijan. The conflict has tested Moscow’s influence in the South Caucasus, a swath of the former Soviet Union it views as vital to defending its own southern flank.