Why was the Mary Celeste found sailing with no one aboard (December 1872)?

The brigantine Mary Celeste left New York for Genoa in November 1872 with Captain Briggs, his wife, their small daughter and seven crew. Her last log-book entry is noon 24 November at 36 56 N 27 20 W; the log slate's last entry is 8 a.m. 25 November, 'eastern point of St. Mary's [Santa Maria, Azores] bore SSW 6 miles'. On 4 December about 1 to 2 p.m. the Dei Gratia found her at 38 20 N 17 15 W, about 375 nautical miles to the east-north-east, under three small sails, on the starboard tack, her one boat gone, 3.5 feet of water in the hold, the pump taken apart and the sounding rod on deck. No one was ever found. Ideas include a false alarm about leaking (abandon ship near land), alcohol fumes, a waterspout, a seaquake and foul play.