"Your guess is as good as mine," said Tom Sayre, a spokesman of The Humane Society for Tacoma and Pierce County.
The outfit included an infant sleeper and a bib that read, "You think I'm cute? You should see my aunt," Sayre added.
An officer found the fawn Tuesday night, said police spokesman Mark Fulghum.
It was unclear how the animal died but the odor indicated it had been dead for awhile, he said.
A Humane Society vet thought it might have been stillborn.
"It's just bizarre," Fulghum said.