Olimpiu Urcan wrote a piece about this in 2005 on the sadly defunct ChessCafe site, with the title, 'Louis van Vliet: Master or Mugger?'
https://web.archive.org/web/20061027204 ... les251.pdf
He assumed that van Vliet was found guilty saying...
...perhaps not understanding the meaning of 'sureties'.Several witnesses as to character gave evidence, but the prisoner was committed for trial. Mr. Vaughan offered to accept two sureties of £25 or one in £50.
The fine he paid was a handsome sum and van Vliet would have been better off if he had won some first prizes at Simpson’s Divan prior to his arrest. Not that this happened frequently; van Vliet scored the occasional victory over some of his higher rated opponents.
However van Vliet was found not guilty.
But perhaps the motive for his odd behaviour wasn't theft, but something rather worse?