To combine the two sentences into a compound sentence, we can use a coordinating conjunction like "and":
Direct Sentences: The thief was punished. The thief was fined.
Compound Sentence: The thief was punished, and the thief was fined.
Explanation: The two independent clauses are joined by the coordinating conjunction "and," which connects the related actions in the sentence.
\boxed{\text{The thief was punished, and the thief was fined.}}