Jimmy Hoffa disappeared 51 years ago today, and his family has not given up hope that the answers to their painful loss will finally come.

"We want the case solved," Hoffa's son, James P. Hoffa, the former five-term president of the International Brotherhood of Teamsters, told Fox News. "The family wants to have accountability for this horrible crime. We want the case solved so that the family can have closure."

Despite the passage of time, the FBI says the case remains ongoing and active. The bureau’s Detroit office is in charge of the case.

"The FBI has worked for five decades to investigate Jimmy Hoffa's disappearance, following every lead and carefully examining all evidence related to this investigation," the bureau said in a statement to Fox News.

"If the public has any new, credible information regarding the disappearance of Jimmy Hoffa, the FBI will investigate," the FBI said.

Hoffa vanished on this day in 1975 as he was on his way to what he thought was a meeting to help his bid to regain the Teamsters union presidency. He was last seen in the parking lot of the Bloomfield Hills, Michigan, restaurant, the Machus Red Fox, at about 2:30 p.m. getting into a car that whisked him away. It is believed that the Detroit Mafia kidnapped and killed him to stop his efforts to take back the union.

The eight-part documentary series, "Riddle, The Search for James R. Hoffa," streaming on Fox Nation, focuses on a dominant theory. It says that Hoffa was picked up at the restaurant by Detroit mob capo Vito "Billy Jack" Giacalone, who, along with mobster Anthony "Tony Pal" Palazzolo, drove Hoffa to a nearby home owned by mobster Carlo Licata and murdered him. His remains were then possibly disposed of in a mob-run sanitation facility in Hamtramck.

Hoffa believes that his father was picked up at the restaurant by Giacalone, but beyond that, he will not speculate about who killed his father.

Fox Nation's "Riddle" series reported that an informant told the FBI that he was present when Hoffa was murdered and said that Giacalone killed him. Such information would have been documented in the FBI records, called 302s, but so far the information has not been made public.

Detroit journalist and mob historian Scott Burnstein, who runs the website "Gangster Report," has confirmed that the 302 exists and reported that "confidential informants" told the FBI "that 'Tony Pal" was the 'doer" in the Hoffa homicide conspiracy, and that Giacalone "headed the Hoffa hit team and was present at the time Palazzolo kidnapped and clipped Hoffa."

Hoffa said that he has been aware of the information that Giacalone murdered his father but cannot confirm that. He does say that his dad was lured to the meeting by Giacalone and his brother Anthony "Tony Jack" Giacalone, who was considered the Detroit mob's street boss. Both men have since died.

In a letter to FBI Director Kash Patel obtained by Fox News, Hoffa wrote last month, "It is important to us and the country that the truth about my father's disappearance (be) told and those involved in his disappearance, even if they are deceased, be exposed."

Through the years there have been a variety of claims about Hoffa's fate.

Fox Nation's series investigated the claims of Frank Sheeran, "The Irishman," which proved to be unfounded. It's also been said that Hoffa's remains were buried in a mob-owned garbage dump in the New Jersey Meadowlands, but the FBI dug at the site in 2022 and came up empty. Stories have circulated that he was cremated or entombed in the downtown Detroit Renaissance Center office building complex.

New claims continue to crop up.

Independent investigator Roscoe Clark told Fox News that he is certain that Hoffa is buried in an undisclosed location in Michigan, and that it would take less than five minutes.

"Forensics will help solve the Jimmy Hoffa cold case," Clark said. "A team of experts is ready to move forward because of a lack of action by law enforcement. A location has been identified within three feet," and he said the necessary locating equipment is ready to be deployed.

The FBI said it has "received countless tips and information from the public, which have been a tremendous help to the FBI. We are grateful to the public, and most importantly, for the Hoffa's family assistance and support over the years."

Observers note that the legacy of Jimmy Hoffa is not what happened to him, but what he accomplished. His hard-fought victories at the bargaining table and on the picket lines enabled generations to enjoy the American Dream, with healthcare and benefits, good pay and retirement. Millions of sons and daughters and their families still benefit from the feisty labor leader's achievements. In some ways, that is how Jimmy Hoffa is still with us, even as he is still deeply missed and mourned by his family.

James Hoffa, his sister Barbara, their adult children and grandchildren somberly mark this day with each passing year.

Every July 30 "is a hard day," said James Hoffa. "We always spend time with it. It is special time, a time to remember. The good thing is, that I had a great father and he did a great job in raising our family. He was a great man and we miss him."

The in-depth series "Riddle, The Search for James R. Hoffa," is streaming on Fox Nation.