John Pena, 30, the other man allegedly pushed onto the tracks, helped pull Williams back onto the platform moments before a train rolled into the station, the New York Post reported.
After the attack, Williams was taken to a hospital, where doctors said he suffered a brain bleed and underwent surgery. He had no brain activity after the procedure, doctors said.
Williams' death has been ruled a homicide.
"I want him to go to the Venezuela prison, the worst place he could go to," his daughter, Debbie Williams, previously told the newspaper. "I want him to suffer for the rest of his life. Prison justice would be appropriate."
She said her father had recently won a five-year battle with prostate cancer six months ago.
Posada-Hernandez, whom the Department of Homeland Security called a "serial criminal," has been deported from the United States four times, the agency said.
"Bairon Posada-Hernandez is a serial criminal and four-time deported illegal alien from Honduras who should never have been able to walk our streets and harm innocent Americans," said Deputy Assistant Secretary Lauren Bis.
Federal authorities are asking New York not to release Posada-Hernandez back onto the streets. New York has adopted sanctuary policies limiting cooperation between local and federal authorities.
U.S. Immigration and Custioms Enforcement has lodged a detainer for Posada-Hernandez. Fox News Digital has reached out to Mayor Zohran Mamdani's office and the New York Public Defenders office.
Posada-Hernandez's criminal history includes 15 prior charges, including simple assault, domestic violence, obstruction of police, possession of a weapon, drug possession and aggravated assault.
He first entered the country Jan. 2, 2008, and has been deported four different times, most recently in 2020. It was unclear when he reentered the U.S. for a fifth time, DHS said.