1) The thief didn't have or hadn't a dirty thumb from the soot on the bottom of the saucepan because he hadn't put his thumb on it. He was the only one who had a clean thumb.
2) His hands didn't get dirty from the soot (is from correct?)CAn you say he didn't dirty his hands with the soot??
1. The thief didn't have a dirty thumb because he hadn't put his thumb in the soot on the bottom of the saucepan.
2. You can phrase it either way.