SEOUL, South Korea (AP) — North Korea on Saturday proposed a joint investigation with the U.S. into the hacking attack against Sony Pictures Entertainment, warning of "serious" consequences if Washington rejects a probe that it believes will prove Pyongyang had nothing to do with the cyberattack. The break-in resulted in the disclosure of tens of thousands of confidential Sony emails and business files, and escalated to threats of terror attacks against U.S.