The memo, released by prosecutor Tim McGinty, said the three women kept daily diaries about being raped, cut off from the outside world and holding on to a glimmer of hope that they would one day reunite with their families.
Castro allegedly told the women that he had other victims and that "some of them made it home, but others had not." The former bus driver once kept the three women locked in a vehicle for three days while he had a visitor at his home.
The victims were discovered in Castro's home in May. They were abducted between 2002 and 2004, when they were in their teens or early 20s. He had a child with Berry during her captivity.
The documents also addressed Berry's 6-year-old daughter, saying her time in captivity started the day she was born Dec. 25, 2006.
"Life is tough, but I'm tougher! Just when the caterpillar thought the world was over, she became a butterfly," Knight wrote.
ABC News' Anthony Castellano contributed to this report.