"I would not call it an aggressive side," she said. "When it came to communication, he had a lot of frustrations. He had language skills, but when he was overwhelmed or over-stimulated, they kind of went out the window. That's why he had staff with him and why she tried to advocate for him and tell the officer what Ethan needed."
Cpl. Jennifer Bailey, a spokeswoman for the sheriff's office, told the Washington Post that Ethan swore and began kicking and hitting the deputies, who were not in uniform.
She said the officers held him down with three sets of handcuffs linked together and removed him from the theater. Ethan landed on the ground and showed signs of medical distress and was transported to the hospital, where he died.
Calls to Bailey at the Frederick County Sheriff's Office were not returned. Reports in the Washington Post indicate that a grand jury declined to bring charges and the three deputies are back on the job.
ABCNews.com called the Maryland Attorney General's office for comment, but they did not return calls.
Saylor said that the police report had numerous statements from witnesses: "Some said that the deputies had their hands on his shoulders and knees and back; and others said they went down on a pile on him. That's why we want it investigated -- there is no explanation in the report how he suffered these fatal injuries."
She said the grand jury concluded that Down syndrome was the cause of death, but, said Saylor, "that's a condition like having an extra finger."
Down syndrome occurs when an individual has a full or extra copy of chromosome 21. One in every 691 babies in the United States is born with the condition, making it the most common chromosomal condition, affecting about 400,000 Americans, according to the National Down Syndrome Society.
"People with Down syndrome as just like everyone else," said Sarah Weir, vice president of advocacy for NDSS. "Some people don't mind people in their personal space and others have a problem with it."
"A lot of what happened with Ethan and the three officers is ignorance," said Sarah Weir, vice president of advocacy for NDSS. "Ethan has a right to be in the movie theater and a right to live independently in his community. He could have been graciously removed from the theater: 'Ethan, want to go get some popcorn' rather than forcing him to the side on the ramp and forcing him down to the ground."
"It's obvious the officers had been poorly trained and if they had been patient, they could have handled the situation completely differently," she said.
Now, Saylor said she feels an obligation to the brother who was so good to her.
"We just want to find the truth," she said. "We want to know what happened through the investigation. There are lots of gaps and holes. This is my brother and this is my family. I am not doing my job as his sister if I don't find out what happened."
ABC News' Mike Levin contributed to this story.