Darius says that the conductor got off the train at 34th Street, while Darius continued on "down the road."
He says he picked up passengers at every stop and discharged the train at the World Trade Center. To Darius, it was business as usual.
"He loved that train so much," Elizabeth says. "He put his heart and soul into it. He wasn't going to do anything to hurt anybody."
That incident led to the first of Darius McCollum's nearly two dozen arrests for his actions related to the transportation system.
"Once he got a taste of that subway train and they let him drive," Elizabeth says, "he wasn't coming home."
She says she had never understood what could be triggering Darius' behavior until his diagnosis of Asperger syndrome in 2002.
In contrast to many individuals who have autism, people who have Asperger syndrome are often adept at communication and have good language skills, Klin says.
Elizabeth says that Darius fits this description. He transferred among several school systems, which Elizabeth says was related to his high intelligence; he was completing junior high-level work when he was only 8.
"He does everything so fast, in a hurry. ... After he finished, he needed more to do," she says.
However, this educational aptitude does not carry over to their communication skills, Klin says, so people who have Asperger syndrome tend to have difficulty with social relationships.
"They are very much at the mercy of others," Klin says. "They are extremely vulnerable to be the victims of pranks."
When Darius was 11 or 12, Elizabeth says he was attacked by one of his classmates, who first tried to scratch his eyes out, and then dug a pair of scissors into his back.
She says that after these incidents, Darius would wake up in the middle of the night screaming, "I see the knife!"
He was beat up by other kids and had his money stolen many times, she remembers. When this happened, he ran out of school.
"Anytime that something happens to him, he runs away," Elizabeth says. "And he runs right to his home, which is in the subway."
Rather than learning to function in the world and interacting with others, Klin says that people who have Asperger syndrome instead collect information about the world.
Sheila Wagner, assistant director at the Emory Autism Center at Emory University, says that this trait often earns people with Asperger's the nickname "the little professor."
But this intelligence can also be the reason why someone with Asperger's may go undiagnosed for many years.
"People see that high cognitive ability and get focused on cognitive potential, but they don't focus on the struggles that they have socially," Wagner says. "Many times [people who have Asperger] slip through the cracks until later."
In addition, until 1994, Asperger disorder was not even listed in the Diagnostic and Statistic Manual of Mental Disorders used by health professionals to evaluate patients.
Even so, getting diagnosed does not mean that treatment can result in a cure.
"There is no medication that is going to make this condition disappear," Wagner says.
However, educational and behavioral therapy can be beneficial, Klin says, adding that people who have Asperger's must be taught the rules of social interaction, such as taking turns while talking.
Also, they must learn to adjust to social cues, such as voice inflection, and to adjust the volume of their speech when necessary.