(NEW YORK) -- New details were revealed Friday about an outside independent probe launched to investigate the treatment of the Turpin siblings since their dramatic 2018 escape from captivity, casting new light on how a Southern California county is grappling with allegations that the 13 siblings have been mistreated under its care.
Nearly four years ago, the Turpin children escaped from their Perris, California, home where they were subjected to brutal violence and deprived of food, sleep, hygiene, education and health care. At the time, advocates and county leaders assured the siblings -- and a concerned public -- that help was on the way. But some officials and some of the Turpin children are speaking out to say they still don't have access to many of the resources and services guaranteed to them.
An ABC News investigation found that some of the Turpin children continue to face challenges and hardships since they were rescued and placed in the care of the county. Some of them have even faced assault and alleged child abuse again.
Watch the Diane Sawyer special event, "Escape From A House Of Horror," on Friday, Nov. 19 at 9 p.m. ET on ABC and stream on Hulu.
In a statement to ABC News earlier this week regarding the Turpin siblings' treatment, Riverside County Executive Officer Jeff Van Wagenen acknowledged that "there have been instances in which those we seek to protect have been harmed," and said his office has hired a law firm to "conduct an independent and comprehensive investigation" into what happened in the cases of the 13 Turpin children.
Officials told ABC News on Friday that Van Wagenen initiated the investigation on Oct. 28, one day after ABC News requested an interview with him to discuss the Turpin case.
As part of the probe, the California law firm Larson LLP "will be seeking" to interview the Turpin children, the county said. Current county employees will be "directed to participate in this investigation," but not required to do so. Former county employees and those who do not work for Riverside County will be asked to cooperate with the probe as well, officials said.
The results of the inquiry will be released publicly when the investigation concludes, which officials said would be in March.
The county has not imposed a budget on the law firm, which "has been instructed to take all reasonable steps consistent with best practices in conducting its investigation," the county said.
Mike Hestrin, the district attorney who prosecuted the Turpins' parents, said the mistreatment of the 13 siblings has exposed serious systemic fissures that exist across the American social services system -- where the most vulnerable should be able to seek help in their time of need.
"If we can't care for the Turpin victims, then how do we have a chance to care for anyone?" Hestrin told ABC News' Diane Sawyer in an interview for the 20/20 special event, "Escape From A House Of Horror."
The investigation into the Turpins' treatment will be led by former U.S. District Judge Stephen G. Larson, who served nearly 10 years on the bench in California, including three years in district court after being appointed by George W. Bush in 2006, according to his bio.
ABC News' Lucien Bruggeman, Josh Margolin and Allison Hope Weiner contributed to this report.