Actually, maintenance is often by third-parties......
Right, but explaining that would have complicated the post.
In the end, it still comes down to the airline, since they are paying the bills and have responsibility for supervising the contractors. My (Retired) Project Manager genes would just love to hear the phone calls back and forth after THIS incident. Talk about the fit hitting the Shan......
When an aircraft incident happens, everyone runs to the log books to see who last touched the airplane. They know within minutes.