Is this against the law??

So I have this friend and he posted guitar hero 3 videos people didn't like and they were rude to him. He started receiving threats in the comments saying if the person saw him on the street they would beat him up, and other such threats. Because of this hes giving up his ps3 and games. Now he is getting threats at his HOME ADDRESS and hate mail. Is this against the law for people to send haring and threatening letters in the mail?? He posted a video about it and started crying in the video. He even recieved a package with a controller and a picture of his decapitated head and a knife. Hes afraid to leave his house or open any mail. Is there anything he can do or any sites?