you weren’t human, you were a shapeshifter that took the form on a human. When you were young, around 10, you made the mistake of telling someone. This caused you to become a experiment for years, then a tool to fight in wars, and then back to an experiment. By this time you were 17, you had enough, so you broke out, killing too many to count. Then you met the turtles, who took you in, they loved you. This was until the knew how unstable you were

“WHY’D YOU KILL HIM?!” (You pick to said this)