Who committed the crime of talking about the secret?
Literal
Secret [object-を] talk crime [object-を] committed [nominalizer-の] [topic-は] who [copula-だ]?
秘密をしゃべる罪を犯した is a complex relative clause: 'committed the crime of talking about the secret.' のは...だ is a cleft construction focusing on the identity of the person.