Gilles de Rais is typically a go-to example. He was a Knight from the Montmorency noble family, and was born in Anjou around 1405. He became a military leader in the 1420s and fought during the Siege era of Orleans against the English and Burgundians during the latter stages of the Hundred Years' War.
Following the end of his career in the mid 1430s he was accused of heresy following allegations of Satanism, and was more alarmingly accused of killing as many as 140 children. Accounts of these acts, obtained though torture, involved abduction and rape, culminating in murder through decapitation or dismemberment and, according to some sources, desecration of corpses by having sex with their exposed organs.
How he was able to take so many children was explained during torture through the use of his position (noble or military) to convince adults to lend him their children, such as asking a tradesmen to send his apprentice over. Following their murder he was able to suggest they had been abducted by bandits while returning to work unaccompanied.
According to an accomplice, his servant 'Poitou', the bodies were typically burnt and their ashes scattered. Much of the gory stuff you can find in Benedetti's biography, which also says that a number of child corpses were found near one of his homes in 1337.
The allegations were found convincing, and he was executed in 1440.
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