I don't know how that got there
You say you don't know how it got there because you're the one who put it there and you're too stubborn to admit it.
"I don't know how that got there", after knocking over a whole shelf of cups.
"I don't know how that got there", after spilling soda on the teacher's desk.
"I don't know how that got there", after throwing a shoe at your brother.