It is medieval Europe. I am second in line to the throne. I publicly murder my brother and his infant son, thus becoming the lawful ruler. What will probably happen to me?

Killing or at least getting rid of family rivals certainly has precedent in the middle ages. William Rufus, one of the most unpopular English kings in history, died in a "hunting accident." King John cloistered his nephew Arthur in a tower, where he subsequently disappeared under suspicious circumstances. Arthur was the son of John's older brother Geoffrey and the legitimate heir to the throne, according to his supporters. St. Wenceslaus, King of Bohemia, was supposedly killed in a plot by his brother. Erik V, King of Denmark, died mysteriously, probably a plot by his political opponents. Louis, Duke of Orleans, was murdered in public by John the Fearless' men, but the population of Paris liked John better. Kings Henry III and Henry IV or France were assassinated as part of the Wars of Religion and the quarrel between the Valois and Bourbon houses. Edward the Martyr, king of the English (probably just Wessex and some surrounding area), was supposedly murdered in a plot by his sister. A handful of Swedish kings have been assassinated.

So what do these have in common? Two major themes - the person in question was generally disliked by the people so the death of their monarch was more of a relief than a tragedy; or there were two somewhat equal factions vying for control who each had a figurehead that had to be dealt with in order to secure power. After all of these, details are much fuzzier. Chronicles of unpopular rulers usually say something about the immoral life the leader led and the harm he brought to his people, so their death was deserved. Others, depending on whose side they were on, say something about there was a great victory for the _____ people or, on the other hand, how a gross miscarriage of justice was executed by the ______ people.

Was any legal prosecution brought against them? Not if you have a sizable army and the other army is now without a leader. Not if you, too, had an equally legitimate claim to the throne - keeping the status quo of the political hierarchy was usually preferable to paradigmatic shifts. Stephen and Matilda's reign in England was such a disaster, as was the Avignon Papacy. Let's take a few later examples to further illustrate the point. Mary Queen of Scots, Charles I, and Louis XVI were all executed via legitimate legal recourse. But why was this possible? Both Mary and Elizabeth had legitimate claim to the English throne, (this situation is way simplified for this post) but Mary was connected to the French throne, had married the unpopular Lord Darnley, and (most importantly) she was Catholic. This made it hard for her to find support in either England or Scotland. Thus, if even though Elizabeth may not have had her executed, there was no one on her side able to stop Elizabeth's supporters from doing so. Charles I lost control of the army, was low on finances, and had lost many of his supporters (again, really simplified). Thus, when Parliament claimed he was committing treason by not acting in the best interest of the English people, there was not enough support left to save him. Finally, Louis XVI was in much the same situation as Charles I, though it was less organized.

There are many more factors involved in these situations, but many political battles in the middle ages came down to who was popular enough to raise the biggest army.

Here are a few books that may help:

(1) Michael Evans. The death of kings : royal deaths in medieval England (2003)

(2) Iam Mortimer. Medieval intrigue : decoding royal conspiracies (2010)

(3) William Jordan. Ideology and royal power in medieval France : kingship, crusades, and the Jews (2001)

(4) Walter Ullman; Brian Tierney. Authority and power : studies on medieval law and government presented to Walter Ullmann on his seventieth birthday (1980)

(5) Joseph Strayer. Medieval statecraft and the perspectives of history; (1971)

(6) PJE Kershaw. Peaceful kings : peace, power, and the early medieval political imagination (2011)

(7) Gwen Seabourne. Imprisoning medieval women : the non-judicial confinement and abduction of women in England, c.1170-1509 (2011)

(8) Bryce Lyon. A constitutional and legal history of medieval England (1980)

(9) Paola Repelli. Symbols of power in art (2011)

(10) Ruth Mazo Karras. Law and the illicit in Medieval Europe (2008)

Hope this helps a little. Happy Reading!