How did ken kaneki turn into a ghoul

kanou decided to transplant rize's organs into him. from then on, kaneki became a half-human, half-ghoul. after the accident, kaneki hid the fact that rize was a ghoul. at that time, he found out that the waitress, touka, from anteiku was also a ghoul when she killed a human in front of him

i guess United States Supreme Court