Going to make this public.

My suggestion would be to just delete and start a brand new account with a strong password. It'll kinda suck having to re-friend everyone, but just in case he might still have access or be able to hack your existing account still.

Well recently there are a lot of those kids out there who know the ways to hack one's account. I've been ha cked before and that guy was actually pretty smart since he changed the email and pass immediatly so I could never get it back, meanies. Well, for now, the solution would be either making a new private account or just change your password and be very careful, there's no real solution to this unfortunately. :/

Make sure to change your email password as well (especially if you use the same for facebook). Make sure you password has: Numbers / Symbols / Different Case letters for added security.

Just have your passwords long enough with upper/lowet caps, number, and symbols. I also suggest using ASCII characters in your passwords. Review your account and adjust your security settings along with privacy settings. Use 2-Authentications (Whatever it's called) if that is available. Be sure all you're passwords for each accounts are different and strong. To see if your email is in a account dump, try out this website. haveibeenpwned.com (Google it if you must) The name is pretty cheesy but it works. If you want to see if a link is malicious, use virustotal. If you want to see if a file is malicious use virustotal. That seems about it that I can think on the top of my head.

Just change your password. My facebook was hacked a while back because my e-mail address got hacked. I changed my password and things are fine now. The police 100% are not going to lift a finger to help you find out who hacked your facebook profile. You would be laughed out of the police station if you brought your computer in for them to investigate. Unless the person who hacked your facebook made death threats towards you or your family, then they will not waste their time. Unless you are a seasoned and professional hacker yourself, you are just wasting your time trying to find the person who hacked your facebook account. Change your password to your e-mail that is linked to your facbook. Change the password to your facebook. Done.