"Your children who have ridaculed [sic] me, who have chosen not to accept me, who have treated me like I am not worth their time are dead. THEY ARE F-ING DEAD," said the note, which was dated 19 April, the day before Harris and Dylan Klebold killed 12 students, a teacher and themselves.
"You need to face the fact that this comes as a result of YOUR CHOICES. Parents and Teachers, YOU F-ED UP. You have taught these kids to be gears and sheep ... I may have taken their lives and my own - but it was your doing. Teachers, Parents, LET THIS MASSACRE BE ON YOUR SHOULDERS UNTIL THE DAY YOU DIE."
Police said they received the manifesto anonymously by e-mail but were taking it very seriously, particularly since it threatened further violence.
"You may think the horror ends with the bullet in my head - but you wouldn't be so lucky," the note concluded. "All that I can leave you with to decipher what more extensive death there is to come is '12Skizto'. You have until April 26th. Goodbye."
A spokesman said investigators had some ideas what the codeword might mean.