HATTIESBURG, Miss. — In the woods off Monroe Road, a truck is so rusted that it is melting into the earth. It was Vernon Dahmer’s truck, the one that he drove and that his family continued to use after his death, the circumstances of which can be inferred from the three penny-size holes in the back panel.

Five men were convicted in the 1966 firebombing and ambush that killed Dahmer, the local NAACP president. But his family is certain about one culprit that went unpunished: the state of Mississippi.

“They’re just as much to blame as the Klansmen,” said Ellie Dahmer, 88, who fled with three children to the barn that night as Vernon Dahmer, her husband, traded fire with the attackers.

So it was with some faith that the Dahmers agreed to hand over parts of the truck to the state, to be exhibited in the Mississippi Civil Rights Museum. Not complete faith, the family clarifies. This is only a loan. And the family has control over its use.

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“If we can’t tell it like it really is,” said Dahmer’s son Vernon Jr., “we best not tell it at all.”

Though several civil-rights museums have cropped up, Mississippi’s will be the first state-operated one in the country. That is its promise: a symbol that Mississippi is reckoning with the ugliest parts of its history.

“It has been a first-class effort, and you don’t see a lot of that in Mississippi,” said Reuben Anderson, the first black judge on the State Supreme Court and a trustee of the Mississippi Department of Archives and History.

But that is also what makes it suspect. For those who were beaten at the hands of state officials, whose oppression was state policy, and who are reminded of that by the Confederate symbol that remains in a corner of the state flag, handing personal relics to the state of Mississippi to become a part of its official history is a loaded decision.

“I know it would be a benefit to the state of Mississippi to have these things,” said Tazwell Bowsky, a black county supervisor in McComb, a town referred to in the early 1960s as the bombing capital of the world. “I know that. But because of the way people have been treated in this state, there will always be suspicion.”

The idea of a privately financed civil-rights museum here goes back years. But in 2011, to nearly everyone’s surprise, Gov. Haley Barbour, a Republican, said a civil-rights museum should be built right next to an already planned state history museum in downtown Jackson, the capital. The civil-rights museum is scheduled to open in 2017.

While there is already a robust collection for the general history museum, the civil-rights museum is another matter. The task of filling it has fallen to people like Cindy Gardner, the director of collections at the Department of Archives and History. Since 2012, she and her colleagues have been traveling around the state, spreading the word that they are looking for historical items from those who lived through the movement years, or from their children.

They insist that the museum will, in the words of Hank Holmes, the director of the department, “not be sugarcoated at all.”

Some whites are skeptical, said Gardner, who is herself white: The museum will cover opponents of the civil-rights movement as well as the people within the movement.

But what Gardner has faced more routinely are sentiments like those expressed by Roscoe Jones, who helped set up the Freedom School in Meridian in 1964. “The trust is not there,” he said.

Perhaps the most high-profile endorsement of the state’s history department came a dozen years ago, when Myrlie Evers-Williams donated the papers of her husband, Medgar Evers, the civil-rights leader who was killed by a sniper at their Jackson home in 1963.

“I believe that if you want history to be truly documented, you have to let go of much of what you have,” said Evers-Williams, 81, now a scholar in residence at Alcorn State University.

She knows the painful intersection of public history and private anguish, which she revisited last year when she first saw an exhibit that will be part of the permanent collection: the hunting rifle used to kill her husband.

“That anger seeped up again,” Evers-Williams said.

Gardner and other officials believe that more artifacts will come in as people see how frankly and seriously the subject is treated.