Orlando (CNN) - Two-year-old Caylee Anthony was able to climb into the family's backyard pool on her own, but she couldn't have installed the removable ladder or opened gates leading to the area, her grandmother testified Friday at the outset of an emotional day in the Casey Anthony murder trial.

Defense attorneys are trying to prove that Caylee could have accidentally drowned in the family pool on June 16, 2008. They argue Casey Anthony and her father panicked when they found the girl's body and covered up her death.

Prosecutors argue Casey Anthony used chloroform to render her daughter unconscious, put duct tape on her nose and mouth to smother her, and then stored her body in the trunk of her car for a few days before disposing of the remains in a wooded field.

But Anthony's defense team has worked intently to call that theory into question in the last few days as the trial rolls toward the end of its fifth week.

On Thursday, Anthony's mother, Cindy Anthony, testified she was using a family computer to search for terms including chloroform and alcohol in March 2008, three months before Caylee disappeared.

She testified Friday about how Caylee was always anxious to get into the pool and how she could climb and descend the pool steps virtually unaided as she approached her third birthday.

Then Anthony's brother, Lee Anthony, took the stand to say that stains in the back of the trunk were there when he owned the car from 2000 to 2005, and probably before. Witnesses for the prosecution have said subtle stains in the trunk of the car could have been made by fluids from the girl's decomposing body.

Later, Anthony and her brother both began to cry when defense attorney Jose Baez asked why he didn't visit his sister in the hospital after Caylee was born in 2005. He said he had only one brief conversation with his mother about his sister's pregnancy until just days before Caylee was born.

"I was very angry at my mom and at my sister," he said. "I was just angry at everyone in general that they didn't want to include me, didn't find it important enough to tell me."