Setting aside the question of whether Israel is or is not guilty of war crimes, why would the ICC need to have Netanyahu in their custody in order to investigate the allegations against Israel? As per the standards of any reasonable criminal court, a defendant cannot be compelled to testify against themselves, so it's not like Netanyahu being in jail in The Hague would help accelerate the investigation. As a person accused of a crime, he would be completely within his rights to refuse to answer any questions and not assist the investigation in any shape or form.

Why not finish the investigation, reach a final verdict, and then issue the arrest warrant? Obviously, Netanyahu should be able to defend himself if charges are brought against him but why does he have to do it from behind bars? The ICC could invite him to testify remotely or in person as a free man, should he feel the necessity to do so.

P.S. This question is strictly about the necessity for an arrest warrant. Let's avoid discussing who's (not) guilty in the war in Gaza, Zionism, Palestine, Hamas or any other tangential topics.