thief or ghost???

just now my youngest sis went upstair...
she tried to open the room door BUT the door is locked!
she asked me to open for her...
i told her it's not lock,open again...

my aunt tried to open for her BUT she also can't open...
i was shocked.i didn't lock the room...
the room doesn't has keys so it was locked from INSIDE!!!!!!!
ah~!!!!!!!!!!!!!!
who's in there?
younger sis said "perhaps it's like last time...
you know~theif....
stupid thief...went in to the poorest room...
we got no money in there....lame...
plus,the room got no door for the thief to run away and all the windows are locked."
(some cage like thingy...)
me:............
thief...what???!
i went upstair and tried to open the door...
BANG IT!!!but still can't opened..
i see through the key hole...
i saw nobody....
my aunt scared...she gone out and came back with lots of villagers!!!
together they kicked,bang and do lots of things to make that door open...
around 10-15 minutes the door opened...
proven it's locked from inside BUT who locked it?!
nobody was in the room!!!
all of them shocked because it is not possible for the door to locked inside itself.
the wind can't do that...wind can only close the door not lock...
inside got two locker...
one of them is the hard to lock type..
need to push very hard to lock it...
how the wind does that??
if there was thief inside...where was the thief?
how the thief managed to get out???
weird......
ghost???????
not possible...
the sun is so bright and the ghost did such lame thing?
crazzzzzzzzzzzzzzy~~~
any idea who lock the door?
let's solve this mystery together...