1173:

Thomas Á Becket canonized

The Archbishop of Canterbury, one-time friend and opponent to King Henry II of England, had been murdered less than three years earlier, and the swift canonization by Pope Alexander III was a clear message of rebuke to the king.

1431:

Public trial of Joan of Arc begins

The trial that had begun in secret in January was at last brought before the public. Joan's request to attend mass beforehand was refused, but she swore to tell the truth and she did so. However, she managed to evade revealing anything she'd said to her king.

Ultimately, Joan was sentenced to death and burned at the stake.

The above events were suggested by John Herrman. Thanks, John!  

1437:

King James I of Scotland

King James the First of Scotland was murdered in the Dominican Friary at Perth by a group led by Sir Robert Graham. James' son, Sir Robert Stewart, was the King's Chamberlain, and it was he who found a willing assassin in Sir Robert Graham, a man with his own grudge and a scarred memory of the imprisonment and banishment. Graham and his eight confederates broke into the room, dragged out the fighting King, and butchered him with twenty-eight dagger-strokes. The Queen was wounded in her efforts to save her husband, and Walter of Atholl, Robert Stewart, Robert Graham and his hired cutthroats were soon taken, and suffered long and appalling torture until the Queen's grief was satisfied and they were sent to the merciful headsman.

This item was submitted by John Herrman. Thanks again, John!

1513:

Pope Julius II