The FBI says it has been working with Sony Pictures Entertainment since shortly after the attacks began. The malware that infected Sony is similar to other malware known to be written and deployed by North Korean actors in the past, down to specific lines of code. The details are sparse, suggesting the evidence itself is either thin, confidential, or both. There are no mention of China, nor any suggestion that any other entities assisted North Korea in the attack. The FBI does not outline any plan for moving forward with action against North Korea following this formal accusation.”]
Source: https://gizmodo.com/fbi-north-korea-was-behind-the-sony-hack-1672489503