Casket Letters found 

Jun.20,1567: The Casket Letters—which directly implicated Mary, Queen of Scots, in a plot with James Hepburn, 4th earl of Bothwell, to murder Mary's husband, Henry Stewart, Lord Darnley—were said to have been discovered this day in 1567.

the eight letters and a series of irregular sonnets asserted by James Douglas, 4th Earl of Morton, to have been found by his servants in a silver casket in the possession of a retainer of James Hepburn, 4th Earl of Bothwell, on June 20, 1567, six days after the surrender of Mary, Queen of Scots, to her rebels at Carberry Hill. If they are genuine—particularly Letter II, or the Glasgow letter—they prove Mary's full complicity with Bothwell in the murder of her husband, Henry Stewart, Lord Darnley, in the preceding February.

The contents of the casket were produced at Westminster, on Dec. 14, 1568, before a body of English commissioners appointed by Queen Elizabeth I to investigate the charges brought by Mary, then a prisoner in England, against the rebel Scottish lords and by them against her. The originals were in French, but translations had already been made into Scottish Gaelic, and further translations were made into English. After the conference, the casket and its original contents were brought back to Scotland and entrusted to Morton's care; a few years after the execution of Morton in 1581, they disappeared—possibly at the hands of Mary's son, James VI.

Whether the letters were authentic or forged preoccupied historians for centuries, with no conclusive results. Even if the letters were completely spurious, however, other circumstantial evidence may be sufficient to indicate Mary's guilt.

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