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LE has
NOT stated definitively either way.
All they have said are a few things that "appears" to be what he's wearing / true of his description.
Not definitively that he "is" - and
not that he's NOT wearing anything else.
If you want to take that to mean he's not wearing a hat definitively, that's fine. It doesn't state that.
And if you want to say he's
ONLY wearing what the description states it
"appears" to depict him wearing, then you'd have to say he's barefoot also since they didn't include footwear.
Obviously that's not the case, though...LE just hasn't stated details they've determined about anything beyond
the most outward things in his clothing that it
"appears" he's depicted wearing.
But he's obviously got more than jeans, a coat/jacket, and a hoodie on - things perhaps slightly less apparent that they've not determined all the details on (like other layers of shirts/things under the jacket, perhaps more outwear like a scarf, footwear, perhaps additional headwear - there's obviously no real physical description of his features in this either - that doesn't mean they don't have that.
It's not intended to be a "he only has on 3 items of clothing" period statement IMO.
The photograph appears to depict a white male wearing blue jeans, a blue coat/jacket, and a hoodie
http://www.in.gov/isp/delphi.htm
https://www.fbi.gov/wanted/seeking-info/liberty-german