Yes, there are some declassified documents related to the incident known as the Battle of Los Angeles. However, these documents do not provide a definitive explanation of what actually happened during the incident.
One of the most notable documents is a memo from the Office of the Chief of Staff of the Army, which was written on February 26, 1942, the day after the incident. The memo states that "the mystery airplanes are still unidentified," and that "no bombs were dropped and no planes were shot down." The memo also notes that the incident was likely caused by "nerves" and "war hysteria."
Another declassified document is a report from the Army Air Forces Intelligence that was written on February 28, 1942. The report states that "the object sighted was probably a balloon, reflecting searchlights," and that "the firing was apparently prompted by a nervous jittery trigger-happy anti-aircraft artillery crew."
While these documents provide some insight into the military's response to the incident, they do not provide a definitive explanation of what actually happened, and the incident remains a mystery to this day.