It should read "The police are going to find out who killed her". Police (in this instance) is plural, and you have no need of the verb to be. Hope this helps.

So, it's sentence. I know you technically can't hear the n but it's there. If you add "be" you're saying the police haven't done the finding of her yet. So you would have to bring "find" in present tense since "is" is in the present tense, like "The police is going to be finding out who killed her." As in saying, they have not started yet. Whereas saying, that I think would be more correct, "The police are going to find out who killed her." or present, "The police is going to find out who killed her." This is saying that the police are in process now of finding out who killed her. So, with be: if you add be, find must be turned to finding. They haven't started finding out yet. Without be: Police are in the process of finding out. (I would say this one is more commonly used. The other one still seems wrong to me even corrected.) I hoped that helped. XD

Hi Viviane, I'm not a native speaker but in my opinion the sentence makes no sense with "be". You're right the correct form is "The police is going to find out who killed her".

Hi Viviane, The correct sentence is "The police is going to find out who killed her" Here, the main verb is "find" and you don't need to use "be" as you'd be using two verbs and that's incorrect. Hope this help.