What can you do if a friend is writing negative things about other people?

i have accidentally discovered my friend`s secret journal. i read it because i couldn`t control my curiousity. she wrote many nasty, unacceptabe things. they are cruel and serious such as my best friend`s boyfriend is a rapist, another one of my friends is having a secret affair with her teacher and the principal at my catholic school is a drug seller who murdered his wife and daughter. i am not sure if those things are true. what if everything she wrote did turn out to be true? what should i do?