Obviously, they can't all be true. In fact, it's pretty unlikely that any version of the story is true, especially considering that the basic premise was borrowed from an older urban legend in which a person (or group of people) high on mushrooms (or acid) captures what they take to be a "gnome" (or leprechaun) and, guess what, locks it in a closet.
This version was posted online in 2008:
A mate was telling us about her friend that lives in a digs in London. His roommate chuned all his housemates that he was gonna get some mushrooms and go trip out in the park. So all the other housemates went out for the day and when they got back home, this guy was lying on the couch still tripping.
He started yelling that there are gnomes in the house and that everyone must be careful. They all laughed it off, but then the guy said, 'no really, I caught one and it is in my room'.
So everyone missioned up to the guy's room and found his closet locked with a chair pushed up against it and something banging from the inside.
...............
When they opened it there was a little down-syndrome kid inside that this guy saw in the park and thought it was a gnome and so he took him home.
And this one in 2008:
This friend of the guy I work with was walking home one night high on shrooms and calls his friend (who is telling the story) and says "man there is a gnome following me man" and the friend says "Its just the shrooms man, its probably just in your head" so the friend on shrooms calls back a second time and says the same thing and the non tripping friend says once again "your just tripping, dont worry, there is no gnome".
Anyways some time passes and they get a third call from their friend tripping on shrooms and he says "Its in my house man and its drinking my milk!" so the friends decide to head over finally and check up on the situation. When they arrive the tripping friend points to his closet and says its in there drinking milk and they open the closet and to their surprise there is a small child with downs syndrome sitting in the closet drinking milk out of a saucer and had been missing for 4 days!
Learn more:
Abducted 'Troll' Incident Is Merely a Tall Tale
Akron Beacon Journal, 20 April 2010
Last updated 09/12/14