I'm going to kill you and you!

My 6 year old was threatened at school yesterday by another 6 year old for no reason. His exact words, I'm going to kill you and you. School left a message on my Husband's phone stating that my daughter had an incident at school were she was harassed. I got this info when my husband got home from work. I couldn't call anyone from school at that time. My daughter never told me anything until I asked her, baby did something happen at school? She said yes mom. A boy at school said he was going to kill me and another girl. My heart hit the floor!!! I asked her did you do anything bad to him or did he get mad at you? She said no mom. So tell me exactly what happened, were where you at when this happened? She said in line getting ready to go home. What face did he make when he told you that? Mad or what. She said, no mom normal. Let me tell you I couldn't sleep all night. I don't take any threat lightly. No matter how old you are, I take it very serious. I'm my mind, I don't understand how a child that age can say the word kill. Maybe kick you, hit you or some other word besides kill. What would you do if your child is threatened to be killed by another child their age?