"The killing of the Congressman at the airstrip had all the earmarks of a professional military hit. How do we know? The eyewitness journalists who wrote of the assassination described it as "silent, calm, brutal, carefully planned and mercilessly executed’" by well-trained killers.
There were never any reliable eyewitness identifications of the assassins. The official government eyewitness, Jim Cobb, admitted to the press that he never even had the shooters in his line of vision! The final tape at Jonestown repeatedly denied any knowledge of the identity of the Congressman’s assassins, and probing further, it said of the people who brought the report from the airstrip, "They saw it happen, and ran into the bush…" In other words, the people from Jonestown were not the shooters, but witnesses. And given the layout of the airstrip, they would have been looking at the shooters’ backs, not their faces. To this day, the assassins have not been identified."
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Shooting a rifle is very easy, and shooting someone at 30 feet is even easier. If they were on an airstrip, you wouldn't need to get nearly so close if you had shot a rifle before. The fact that the pilot and co-pilots escaped indicates that they were either let go (why?) or this was sloppy and botched. And why would they make noise? Shotguns at 30 feet are pretty basic. Jackie Speier (http://en.wikipedia.org/wiki/Jackie_Speier) was shot 5 times and lived to tell about it (http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/11/16/...). Someone wanted her dead enough to shoot her at close range, but didn't know how to do it properly.
I'm going with Occum's Razor on this one.