Complex sentence: He admitted to the government that he was guilty only of the plot's concealment, denying that he had ever been an active member of the conspiracy, although by the end of the month he had admitted his involvement in the Spanish Treason of 1602--1603.
Split into simpler sentences: He admitted to the government that he was guilty only of the plot's concealment, denying that he had ever been an active member of the conspiracy. Regardless of the scale of his involvement he was guilty at the least of concealment of treason, and by the end of the month he had admitted his involvement in the Spanish Treason of 1602--1603.