It could have been North Koreans but not connected to the government. According to security expert Bruce Schneier, “reusing old attack code is a sign of a more conventional hacker being behind this.” There is consensus among security experts that there was nothing about this hack that required the resources of a nation-state.

Both the US Government and Sony Have Political Reasons to Blame North Korea

Sony faces the possibility of numerous lawsuits as a result of sensitive data from employees, ex-employees and various partners being exposed. According to Jonathan Zittrain, professor of law and computer science at Harvard University, Sony might have some immunity from these lawsuits if this attack was part of an act of war.

via Why Security Experts Are Skeptical that North Korea Masterminded the Sony Attack – Business Insider.