As a Class-3 Dealers back in the 9170s, I can tell you that a 'silencer' not making hardly any sound is more Hollywood movie myth/lore than it is in reality. The device suppresses the report of the round being fired and in small caliber weapons it can be near silent with single shots.
Without out knowing the caliber and type of 'machine gun' the shooter used makes it harder to offer a sound assessment without generalizing.
However, yes, you can put a suppressor on a fully automatic rifle caliber weapon but firing fully automatic as the shooter apparently was doing, the suppress would wear out very fast.
Sorry--