During the reading of a paper, published in the proceeding of a prestigious computer science conference, I noticed a logical error in the results presented in the paper.
I contacted two of the authors who are my colleagues (one is a PhD student in the same lab where I am a student) to ask for clarification. After hearing what they had to say, I was under the impression that they mainly tried to convince me that the results were OK. One argument they used was that because the paper was already published in a prestigious conference and passed the peer review, the results couldn't have been wrong. That didn't satisfy me; rather, their answers made me suspicious that at least parts of the results, presented in the paper, are fake (I mean, are not real). Moreover, that the authors tried to hide the problem with the results. Finally, I believe I have strong evidence to support my belief, which, at the moment, is that the results are fake.
What is the normal course of action in a case like this? If someone has some evidence indicating that a paper published in proceedings of a (computer science) conference includes fake results, what should that person do?
It's been more than two years since the paper was published.
The evidence that the paper is "fake" rather than merely wrong is that the method claimed would not be computationally tractable for the claimed data size without some special innovation that was not described by the authors.