Officials also announced on Wednesday what they said was the final extension to a voluntary disclosure program under which prosecutors would agree not to bring criminal charges or file civil lawsuits against any Long Island Rail Road retirees who admitted they had been awarded Railroad Retirement Board disability benefits by making false statements and who agreed to give up certain benefits.

“If you are an L.I.R.R. retiree who lied to get disability benefits, the deadline for participation in the early version of the voluntary disclosure program is upon you,” Preet Bharara, the United States attorney for the Southern District of New York, said in a news release. “But make no mistake — there is no deadline for concluding our investigation. We are both relentless and patient and will continue to aggressively investigate this.”

Prosecutors have said hundreds of retirees took part in the multiyear, systemic fraud to obtain the Railroad Retirement Board disability benefits. The deception, they have said, was carried out with the assistance of people whom prosecutors identified as “facilitators” — liaisons between retiring workers and doctors, who falsely declared retiring railroad workers to be occupationally disabled.

Eleven people, including retired railroad workers, doctors and a pension agency employee, were charged in 2011 with taking part in the scheme, in which the retired workers falsely claimed to have disabling injuries, entitling them to higher pension payouts. Most were charged this spring.