(ABC News) -- Michelle Knight, one of three women who survived more than a decade of captivity in Ariel Castro's Cleveland house, was so emaciated that the rescuing police officer initially thought she was a little girl.
She was also so scared that during her rescue she had trouble breathing.
That portrait of Knight, who is believed to have suffered the most abuse at the hands of Castro, was detailed by police at Castro's sentencing hearing today.
But before the hearing began, Knight declared that she was no longer that battered and terrified person.
"Just when the caterpillar thought the world was over, she became a butterfly," Knight wrote on the eve of Castro's sentencing hearing. Her message was posted on the Cleveland police department's website.
"You don't know how much I appreciate all your time and work collecting cards and gifts from people for me and the other girls. I am overwhelmed by the amount of thoughts, love and prayers expressed by complete strangers. It is comforting. Life is tough, but I'm tougher!" she wrote.
Knight, 32, not only issued a statement of gratitude, but is expected to be the only one of Castro's three victims to appear in court today to personally read her impact statement before her tormentor is sentenced to life in prison plus 1,000 years.
Her fellow captives Amanda Berry and Gina DeJesus submitted statements that were read by others.
Psychiatrist Dr. Frank Ochberg said the court today while mentioning Knight, "What an extraordinary human being." He said she served as doctor and nurse to the other two women and a child born in captivity.
Ochberg called her a "very courageous and heroic individual."
During this morning's hearing, testimony by police officers hinted at the horror Knight endured.
Knight was 22 when she was snatched off the street by Castro. She was held the longest along with DeJesus and Berry, and appeared the bear the brunt of his wrath.
She was captured by Castro, officials testified, when she was searching for the office of her social worker to discuss the custody of her 2-year-old son. She was lost and asking for directions in a store. Castro stepped forward and offered to take her there, police testified.
On the way, he stopped at his house and asked Knight if she would like to pick up a puppy to take to her son, and Knight agreed. But inside, Castro restrained her with an extension cord, dragged her to the basement where he bound her with chains, put a motorcycle helmet on her and began more than a decade of rape and battering.
Knight told the court that she "cried every night."
"Christmas was the most traumatic day because I never got to spend it with my son," she told court, her composure cracking slightly.
She told Castro, "I will live on, but you will die a little every day." She also told him, "I can forgive you, but never forget."
Officer Barbara Johnson, who entered the house earlier this year to rescue the three women, said that when she ventured to the second floor of Castro's house Knight jumped into the arms of herself and another police officer, wrapping her arms and legs around the officers.
"Michelle was so tiny I thought she was a little girl," Johnson said. It wasn't until she was able to pry Knight off of her that she realized Knight was a "grown woman."
"She was very scared," the officer said. "She had a difficult time breathing."
In police affidavits released after his arrest, Knight told police that she became pregnant by Castro several times and each time he forced her to abort by starving her for weeks and then punching her in the stomach.
Officers today said that it went beyond punching, saying the Castro would jump on her and kick her in the stomach and once pushed her down the stairs to force a miscarriage.
Dr. Gerald Maloney was ER doctor when the women were hospitalized after their rescue and said that Knight appeared to be suffering from malnutrition.
All three girls were upset, he said.
"Michelle in particular appeared very upset and did not want a male doctor or nurse" taking care of her, Maloney said. Female staff were brought in to examine and care for her, the doctor said.
Documents released Wednesday by prosecutors revealed that there is a federal probe into thousands of dollars in Social Security checks cashed in Knight's name while she was a hostage.
The Social Security checks are believed to Supplemental Security income provided for adults and children with low income and who have disabilities.
Knight was described by family members as having a mild disability and was the mother of a young son at the time of her disappearance.
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