"I don't know who the new mayoral candidate is."
Translation:Saya tidak tahu siapa calon wali kota yang baru itu.
This use of "itu" seems to pop up maybe every other week for me here, and it always gets these same puzzled questions from users including me.
I don't doubt that it's legitimate Indonesian, but I've NEVER seen a satisfactory or helpful explanation. Only conjectures from other well-intentioned non-native speakers.