JACKSON (AP) — Federal authorities will continue to investigate the 1964 Mississippi killings of three civil rights workers — a case that helped pass landmark legislation — despite the death of a key suspect, the Justice Department says.

Billy Wayne Posey, 73, died Thursday. Federal investigators were looking into his possible involvement in the June 21, 1964, killings of James Chaney, Andrew Goodman and Michael Schwerner, who had been working to register black voters.

Posey’s funeral was Saturday in Philadelphia, Miss., the town at the heart of the case.

On Friday afternoon, Alejandro Miyar, a spokesman for the Justice Department, said the death does not ‘‘alter our cold-case investigation.’’

He said federal authorities are assisting state investigators who could bring state charges.

Goodman’s brother, David Goodman, of New York City, said, ‘‘This is still the country of law and order, and the laws are clear. There is no statute of limitations on murder.’’

The slayings shocked the nation, helped spur passage of the landmark Civil Rights Act of 1964 and were dramatized in the 1988 movie ‘‘Mississippi Burning.’’

In the summer of 1964, hundreds of FBI agents investigated the trio’s disappearance, leading to the discovery of their bodies buried 15 feet beneath an earthen dam.

In 1967, 18 men went on trial for conspiring to violate the civil rights of the three victims, and seven of them were convicted.

One of the seven, former Neshoba County Sheriff’s Deputy Cecil Price, told authorities before his 2001 death that he told Posey in 1964 he had just jailed the three civil rights workers on a traffic charge and asked Posey to get in contact with Edgar Ray Killen, who helped to orchestrate the killings.

The only murder prosecution took place in 2005 when a Neshoba County jury convicted Killen, a reputed Ku Klux Klan leader, on three counts of manslaughter. He is serving 60 years in prison. Civil rights activists have been pushing for more murder charges.

Authorities have said at least four suspects remain alive.

In a 2000 statement, Posey told investigators there were ‘‘a lot of persons involved in the murders that did not go to jail’’ but he did not identify them.

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Information from: The Clarion-Ledger, http://www.clarionledger.com