Complex sentence: The investigation was a "scoping exercise" aimed at a "preliminary assessment of the evidence rather than a formal inquiry", and the existence of the "assessment" operation was confirmed only on 12 December 2012 after operating in secret for several weeks.
Split into simpler sentences: The investigation was a "scoping exercise" aimed at a "preliminary assessment of the evidence rather than a formal inquiry". The existence of the operation was confirmed on 12 December 2012, after operating in secret for several weeks.