Well according to a report from The Security Ledger, that very well could be the case. The report covers the claims of security research Norse who states that they have found evidence that it could be an inside job. Norse found the evidence within the leaked human resource documents that was released as part of the hack, and actually followed that suspect by tracking her online activities for the past few months.
They found that this particular employee had a very technical background and that following her layoff, she had made several angry posts on social media about her losing her job and about Sony. They also discovered that she had made connections with other individuals who are affiliated with the underground hacking scene and hacktivist groups based in Europe and Asia.
Now it is possible that this former Sony employee could have helped North Korea with their attacks, if they were involved at all, but safe to say unless Sony or an official source confirms it, it is just speculation for now, but what do you guys think?