It was Saturday, and Gordon Klein's three younger brothers wanted to go to Farview Park, four blocks from their north Minneapolis home. Gordon, age 9, first wanted to fix his knife sheath, so he told them he'd meet them later under a big oak at the park.

When Gordon got to the park, his brothers were nowhere to be found. He searched the playground. No trace. They had vanished.

Police and Boy Scouts searched door to door, using a dog to track the boys' movements. Nothing. Three days later, a railroad worker spotted two of the boys' plaid woolen caps on the Mississippi River ice near the St. Anthony Falls dam. Police ruled the case an accidental drowning.

After Nov. 10, 1951, Gordon never again saw 8-year-old Kenneth Jr., 6-year-old David and 4-year-old Danny. His guilt would consume him for the next 68 years, according to Minneapolis author Jack El-Hai's new book, "The Lost Brothers: A Family's Decades-Long Search."

"As the oldest, Gordon always considered himself the boss of the brothers," writes El-Hai, who has tracked the case for more than 20 years. "It pained him to think about his missing siblings. He wished he hadn't stayed home fixing his crappy old knife sheath, and he replayed the tragic day's events in his head.

"Go with them, he urged himself in his reimagining. Be there at their side. Whatever happened to his brothers, he knew it wouldn't have happened if he had just walked to the park with them."

Though El-Hai's book and a companion TPT podcast focus on the missing Klein boys, Gordon becomes the story's central character, keeping the heartache of an old tragedy painfully alive.

"I know they wouldn't have went anywhere without me," Gordon says on the podcast trailer. "They sure wouldn't have went in the river, I can tell you that."

Now in his late 70s, Gordon Klein lives in Elk River, where he is retired and hauls gravel in his truck as a hobby. For years he ran a millwright business with his wife of more than three decades, Diana. Now he wonders, El-Hai writes, what his life might have been like had his brothers not disappeared.

"We could get together and do things," he told El-Hai — maybe trade stories about the raccoon they adopted and fed with an eye dropper, or sledding down the hill at the park. "You know, what people do when they get older," Gordon said, adding: "I do feel guilty."

From the beginning, neither Gordon nor his late parents, Betty and Kenneth Klein, believed the boys drowned. Police who have reopened the case over the years also doubt the drowning scenario. None of the boys' bodies ever turned up.

Their father, a Northland Milk Co. mechanic, always maintained the plaid caps were placed on the river ice to throw off cops, possibly by the boys' abductor.

"It is hard to believe no bodies would ever surface or be found," Wright County Sheriff's deputy Jessica Miller told El-Hai. "The odds of that are so slim."

Miller is one of several investigators who've tried to crack the mystery in recent years. According to the book, Minneapolis Park Police Sgt. Jim Schultz told WCCO-TV the drowning theory was "an injustice — a bad conclusion." Retired Hennepin County Medical Examiner Garry Peterson said the odds are close to one in a million that three boys could go in the river and never surface.

So what happened to Kenny, David and Danny? El-Hai doesn't solve the case or wrap it up with a bow, but he does offer several possible scenarios and suspects. Three rise to the top:

• Four years after the Klein boys' disappearance, a former playground worker at Farview Park came under investigation in Illinois for the murder of three Chicago boys. The park worker, who had moved away from Minneapolis shortly after the Kleins vanished, died in 1962.

• A woman dying of cancer about 15 years ago told a private investigator hired by the family that she rented rooms in the area to a "creepy" man in his 50s and a teenager. She saw them playing basketball with some boys when the Kleins went missing, but kept quiet out of fear of the older renter.

• Then there was a truck driver who lived close enough that the boys could have cut through his yard on the way to the park. Soon after the Kleins disappeared, he reportedly poured a new concrete floor in his basement and replaced the bed of his pickup truck. A decade later, a woman came forth saying he had molested her 5-year-old daughter in the 1950s. He died in 1975.

Betty and Kenneth Klein moved to Monticello, Minn., three years after their sons disappeared and had four more boys. They baked birthday cakes for the missing boys on their birthdays, bought Christmas presents in case they returned and visited schools across the state to see if they had been abducted and adopted by another family.

"I don't know what happened," Gordon told El-Hai. "I think they truly met someone who took them around," someone they may have known. "But you know, you think a lot of things."

Curt Brown's tales about Minnesota's history appear each Sunday. Readers can send him ideas and suggestions at mnhistory@startribune.com. His latest book looks at 1918 Minnesota, when flu, war and fires converged: http://strib.mn/MN1918.