1. He may have stolen the money.

Question

2. He might have stolen the money.
3. He can have stolen the money.
4. He could have stolen the money.
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Is #3 ungrammatical? Are #2 and #4 the same in meaning? They both have slight or uncertain possibility. Is that right? #2 has slighter probability than #1, doesn't it?

Answer 1

#3 would not be used.

The other three sentences mean approximately the same thing.