My family's safety threatened

My 8 year-old-son came home today and told me that one of the troublemakers who is also in his class at school told him that he was going to burn our house down, he and his 14 year old brother. My son is now terrified.

This is the 3rd time this little sh!t has bullied my son. In year 2 he physically assaulted him for several weeks until he had a breakdown. In year 3 her threatened him with physical violence and made him ill once again and now in year 4 he is threatening to burn our home down! What gets me the most is 8 year olds aren't that sinister - he has picked this up from somewhere meaning someone in my neighbourhood is talking about burning my house down.. it could be another child or it could be an adult - either way, it is very frightening. I'm taking this further - they are not getting away with this - my poor son is having nightmares as I type - this is so wrong!!!