A gaunt 18-year-old Georgia man told California police his stepfather had banished him and sent him on a cross-country bus ride after the stepfather had confined him to a room for four years, authorities said.

The confinement allegedly was so thorough, Mitch Comer's two younger sisters – living in the same home – hadn't seen the teen for the last two years, and he says he hadn't been outdoors in at least that amount of time, Paulding County (Georgia) Sheriff's Cpl. Ashley Henson said.

The teen's stepfather and mother were arrested in Dallas, Georgia, last week after a retired Los Angeles police officer found the teen wandering an L.A. bus station, weighing under 100 pounds at just over 5 feet tall, and looking like he was 12 or 13, the L.A. Police Department said.

Paul M. Comer, 48, and the teen's mother, Sheila M. Comer, 39, both of Dallas, Georgia, were charged last week with cruelty to children relating to alleged abuse during Mitch Comer's minor years, Henson said. Both are being held without opportunity for bail, pending an October 4 hearing.

"The information we have is … the neighbors didn't even know there was a boy living in the home," Paulding County District Attorney Dick Donovan told "CNN Newsroom" on Friday.

The investigation started on September 11 when retired LAPD Sgt. Joe Gonzales, working security at an L.A. Greyhound bus station, called police after mistaking Mitch Comer for a child wandering the station alone, police said.

The teen told officers that Paul Comer had kicked him out of his Georgia home because he had just turned 18. Comer drove him to a Jackson, Mississippi, bus station, gave him $200 and information on Los Angeles homeless shelters that he gleaned from the Internet, put him on a bus and told him never to return, authorities said.

The teen also told investigators he was abused at home for the last four years, saying that after Comer removed him from school in the eighth grade, he was confined to a room and given small amounts of food daily.

He also said he was forced to "assume a grueling disciplinary position every day for eight hours, with the top of his head against a wall, his fingers interlaced behind his head and his feet raised off the ground," the L.A. Police Department said.

"He saw the mom and the (stepfather), but he hadn't seen the sisters for two years," Henson said.

Mitch Comer told investigators he lived mostly in Georgia, though the family moved to Arizona and perhaps other places before returning.

After Los Angeles police contacted Paulding County authorities, Paul and Sheila Comer were arrested, and the teen's sisters – ages 13 and 11 – were put into protective custody, Henson said.

One of Donovan's investigators flew to Los Angeles and escorted the teen back to Georgia, where a family volunteered to take him in "until we can get things moving or … find a better placement," Donovan said.

"According to my investigator whom I sent to L.A. to pick him up and take him home, he is a very sweet, very polite young man who loves to read, and who said that his greatest desire is to just live a normal life," Donovan told "CNN Newsroom."

Henson said the charges against Paul and Sheila Comer relate only to the 18-year-old. Investigators have yet to speak to the girls in-depth, Henson said.

Sheila Comer's attorney, Renee Rockwell of Atlanta, said Friday that her client will plead not guilty. She said that she couldn't say a lot about the case yet.

"The investigation is just starting. I'm sure there's a lot that is going to come out sooner or later, just a lot of facts that have yet to be disclosed to the public," Rockwell said Friday.

Paul and Sheila Comer have not had any contact with each other since the arrests, Rockwell said.

A call to the office of Paul Comer's attorney, W. Scott Smith of Atlanta, wasn't immediately returned Friday.

The FBI and the Georgia Bureau of Investigation are among the agencies investigating the case, Henson said.

Henson said his department wants to give "all the credit to retired Sgt. Gonzales" and the Los Angeles Police Department for flagging the case.

"Without (Gonzales') watchful eye and his experience, (Mitch Comer) might never have been found, and he might not have survived," Henson said.

– CNN's Brooke Baldwin contributed to this report.