I suspect that both helped; but Craigslist struck the more architecturally brutal blow.
Unless newspapers actually used to be sustained by subscribers, and all those ads were just to pad the margins, Craigslist and its ilk can largely gut the newspaper and watch it bleed out without ever doing something newspaper-like.
Online news sources, by contrast, tend to be more convenient(and, to a debatable but probably nonzero degree, probably coast a bit on the activity of traditional news organizations); but they are in the business of providing a similar product through different channels.
If news gathering cannot survive without a (more or less artificial) connection to advertising and transaction handling, which are clearly handled better by other entities, it's absolutely dead.
If news distribution is something that people don't want to do on paper, and the existing outfits can't change, there is at least theoretical room for somebody to build on the ashes.