Call it Al Capone’s final haul. A trove of family mementos, jewelry and weapons that were once owned by the notorious gangster will be auctioned off by his three surviving granddaughters, who lived in relative obscurity until they emerged in 2019.

The collection, which includes Capone’s “favorite” gun (a Colt .45 pistol starting at $50,000), a Patek Philippe pocket watch monogrammed with 90 diamonds, and personal letters is estimated to sell for $700,000, by luxury asset auctioneer Witherell’s, based in Sacramento, which revealed the catalog today. Timothy Gordon, of PBS’s “Antiques Roadshow,” appraised the items.

“Al Capone is the most-collected historical figure in the criminal world, and traditionally his items have sold at astronomical amounts,” said Mr. Gordon. Personal items, especially monogrammed, perform particularly well, experts said. In 2017, a diamond watch owned by Capone sold for $84,375, more than tripling its pre-auction estimate. A 2014 Sotheby’s auction sold Capone’s engraved 1932 silver-plated cocktail shaker for roughly $68,500.

This latest batch of items comes at a time when there is renewed focus on how the culture and market value objects of historical significance but moral murkiness. “Some people buy Nazi paraphernalia for the purpose of taking it off the market,” said Erin Thompson, a professor of art crime at the John Jay College of Criminal Justice. “I would feel uncomfortable putting up for sale something that doesn’t benefit victims. But this Capone collection gets at bigger questions buyers and curators are asking now: Who do we want to honor in American history? Whose lives are of interest? Whose possessions are of interest?”

Capone’s granddaughter, Diane Pette, a retired counselor at Mission College in Santa Clara, Calif., said she and her sister Barbara decided in January that the time was right to unload the collection. “We were getting older and we were concerned that if anything happened to either of us, that people wouldn’t know what was what and what was the story that went with each thing,” she said. She also worried that some of the collection might be damaged by the wildfires that have recently burned much of Northern California; last year, her home in Auburn, Calif., was under threat of evacuation.

The sale comes 74 years after Capone’s death, and plays on his broader mythos and iconic sense of style. The popular caricature of a cigar-chomping gangster decked in a fedora and pinstriped suit is patterned on Capone. He also had a famous sense of indulgence. His first prison cell, at Pennsylvania’s Eastern State Penitentiary in 1929, included a desk lamp on a polished desk, “tasteful paintings,” and “a powerful cabinet radio receiver of handsome design and fine finish,” according to a local newspaper article of the time.

“Unlike the Al Capone safe, we know exactly what’s in this collection,” said Brian Witherell, consignment director of his family’s eponymous auction house, referencing “The Mysteries of Al Capone’s Vaults,” an anticlimactic live television event in 1986. During the TV special, journalist Geraldo Rivera came up empty-handed in the search of a vault purported to be Capone’s.

“I doubt that [1930s] businessmen would walk around with such gaudy items as Al Capone carried around with him,” Mr. Witherell added while flagging the collection’s pristine provenance as its biggest draw.

Not everything in the collection is ostentatious or provocative: Capone’s marital bed frame and humidor are selling for starting bids of $1,250 and $2,500, respectively. There is also an extensive collection of porcelain figurines. Mr. Witherell guessed the figurines would sell for between $50 and $75 in everyday circumstances, but their possession by Capone increased their value to between $250 and $500, he said.

Mario Gomes, an optical technician for Costco in Montreal who runs an online museum dedicated to Capone and is widely recognized as an expert on him, suggested that the guns were unlikely to be used in crimes because their serial numbers are intact—“especially the ones that he kept in his family,” he said—where an experienced criminal might have removed them.

“People made up stories that he had a gun in his hand right out of the womb,” said Mr. Gomes, emphasizing: “It’s not true.”

Ms. Pette kept two items for herself: a ring that belonged to her grandmother and a shot glass belonging to Capone. “Most of our treasures are things we hold in our hearts,” she said. “We came from an extremely loving family, and that’s the greatest treasure that we have.”

A loving grandfather isn’t how most Americans remember Capone.

“The first question is: Is Al Capone the kind of criminal for whom we think that he ultimately paid whatever debts he had to society?” said Nien-hê Hsieh, a Harvard Business School professor who is also the acting director of the university’s ethics center. “He did go to jail and was released from jail.”

Erich Hatala Matthes, an ethicist who wrote “Drawing the Line: What to Do with the Work of Immoral Artists from Museums to the Movies,” said there is still value in historical items that have been wrapped up in violence. “It’s not a worthwhile question to ask of a collection of objects: Are these ethically pure?” he said. “Knowing this is Al Capone’s stuff is enough to have moral concern.”

Then there is the matter of curiosity. “I might go,” said Mr. Matthes of the sale, “just to see what happens.”