As far as I know Lew Powell didn't even own a night shirt while working with JWB and the conspirators - could have, but most soldiers slept in their drawers - which is probably what Powell did. Weichmann seen him unpack his carpetbag upon his 2nd visit to the Surratt Boarding House and claimed that he had three linen shirts and a linen coat - now, it could be that one of the linen shirts was a night shirt; but we simply don't know. There is no record that Lew left anything behind in either Branson House or Herndon House - and all he left behind in Northern Virginia was a diary and photograph (still looking for those!) and several horses branded "US" which he captured while with Mosby.....
So, no - it's not Lew Powell.....
"The Past is a foreign country...they do things differently there" - L. P. Hartley