HR is on the wrong here, police is not required to discuss judgement if someone is innocent or not (anyways Its the court which decides), they investigate and compile evidence, And they are not required to Answer to a 3rd party especially if the investigation is ongoing.
Policeman didn't want to share his insight with HR but he felt entitled. Threats like IG will call and stuff is the Bullshit IK is trying to eliminate, no one can threaten a policeman doing his job. Some kind words from HR like "will you please share your thoughts on this matter"? would have helped, but unfortunately good manners are scarce.