NATO is running a complex propaganda campaign against Russia. It includes several elements, like accusations that Russia interfered in the US elections; intervened in Ukraine and Crimea; threatens German elections and European democracy. An important component of the campaign is the statement about Russian involvement in the MH17 tragedy.
The mentioned conclusions come from various credible sources, and are not originally NATO statements (although NATO agrees with the conclusions). The US intelligence agencies have concluded that Russia interfered in the US election http://nyti.ms/2iO7d5e, the International Criminal Court has concluded that Russia intervened illegaly in Ukraine http://bit.ly/2ftv6iT, Angela Merkel and German intelligence have stated that Russia's interference can threaten German elections and democracy http://bit.ly/2jPBdNu. Russia's involvement in the MH17 tragedy has been proved by the independent investigation by the JIT http://bit.ly/2d980Nz.