Manager showing favoritism, should I stay out of it?

In another department the manager has hired his friend as a temp. This temp does nothing all day but hide in the restroom and sit in the manager's office acting like he's reading SOPs. Now the manager has given this temp passwords to access information that only permanent employees should know. (he bragged about it to me). The other permanent employees are complaining to me. I see all this with my own eyes but I do not work in that department. I told them that wasn't my business and they need to talk to HR, but for some reason they are all afraid. What do you think I should do? They are being treated unfairly but I'm tired of everyone complaining to me.