When the chief prosecutor of the international criminal court (ICC) announced he was seeking arrest warrants against Israeli and Hamas leaders, he issued a cryptic warning: “I insist that all attempts to impede, intimidate or improperly influence the officials of this court must cease immediately.”

Karim Khan did not provide specific details of attempts to interfere in the ICC’s work, but he noted a clause in the court’s foundational treaty that made any such interference a criminal offence. If the conduct continued, he added, “my office will not hesitate to act”.

The prosecutor did not say who had attempted to intervene in the administration of justice, or how exactly they had done so.

Now, an investigation by the Guardian and the Israeli-based magazines +972 and Local Call can reveal how Israel has run an almost decade-long secret “war” against the court. The country deployed its intelligence agencies to surveil, hack, pressure, smear and allegedly threaten senior ICC staff in an effort to derail the court’s inquiries.