I think basically Newsweek would claim "we did all this research and a lot of points to this guy as being the guy. Our news story doesn't say "this guy is the guy, our news story lays out the evidence and says we think this is the guy based on this evidence."
Fair? Maybe not, but I'm guessing the newspaper's free speech rights cover their ability to investigate and speculate as long as they are clear about the fact that they are indeed speculating. It's a question of ethics and credibility as to whether the evidence is of enough quantity and quality that they should publish a news story speculating.