Does 'washing himself' mean 'taking bath'?

Question

In The Adventures of Tom Sawyer by Mark Twain, there is a line:

A gory knife had been found close to the murdered man, and it had been recognized by somebody as belonging to Muff Potter— so the story ran. And it was said that a belated citizen had come upon Potter washing himself in the "branch" about one or two o’clock in the morning, and that Potter had at once sneaked off -- suspicious circumstances, especially the washing which was not a habit with Potter.

Does 'come upon' mean 'having come to meet'? Does 'washing himself' mean 'taking bath'? But then why would Potter sneak off?

Answer 1

1. "Come upon" means an encounter by chance, not a planned meeting.
2. "Washing" could be immersing just hands or other body part, or it could include bathing. But Clemens chose the more general "washing", so there;'s no reason, a priori, to assume it means "bathing" (though "bathing" could also mean one body part, if that part is mentioned).
3. If Potter does not have the habit of washing, why might he not wish to be seen doing so in these circumstances? That is the point of this narrative.