For what reason would aliens want to come to earth? I've composed a list; all could be truths. Well, maybe...
Anything Odd, Scary or Plain Funny aliens
A German printed pamphlet a witch hunter's manual, Malleus Maeficarum. It included the details on how to handle werewolves if one should be caught. Sixteen pages long, published way back in 1590 with no copies surviving but, two copies of the English version do exist, deep down in the vaults of the British Museum and the Lambeth Library.
In 1920 a gentleman by the name of Montague Summers rediscovered the lost pamphlets which describes the life and times of Peter Stumpp, a rich farmer, a serial killer and a cannibal, alias the;
"Werewolf of Bedburg."
His last name Stump spelt Stumpf in German, arose after a werewolf was allegedly caught in a trap and had to chew his front paw off to escape, which proved Peter Stumpp a werewolf. People forgot he had lost his hand in an accident, years earlier.
In 1589, Stumpp was accused of being a werewolf, leading to the most famous werewolf trial in history. He was found guilty, stretched on a rack and tortured, he confessed claiming that;
"the Devil made me do it!"
Giving him the power to change into a wolf by using a mysterious belt; you put it on you become a wolf, take it off you become a man again.
Under torture he confessed to killing and eating fourteen children one of whom was his own son, he relished eating his brain and two pregnant women devouring the unborn fetuses,
"their tiny hearts still pumping, hot and raw."
His daughter and mistress a distant relative were also sentenced to death for having an incestuous affair with him. This is supposedly what happened at the execution. He was put on the wheel and flesh was torn from his body in ten places with red hot pincers. His limbs were broken with the blunt side of an axehead, then he was beheaded and burned along with the flayed and strangled bodies of his daughter and his mistress. Finally, his severed head was displayed on a pole to warn others, this type of behaviour will not be tolerated.
The werewolf trial was basically a political trial for the new Lord of Bedburg, Count Salm-Reifferschedt-Dyck a Catholic, to control and bully the Protestants. It was just another execution of a werewolf and a couple of witches. Case closed.
ref: The Werewolf of Bedburg
for details of the murders: Science Fiction Chronicles