Mail addressed to Nicholai Dahl and his daughter, Aagot, started stacking up at the post office in tiny Quiring, Minn., in the early spring of 1904. That was the first hint that something was amiss in the North Woods crossroads, about 15 miles northwest of Blackduck in Beltrami County.

White-haired widower Dahl, 56, was a Norwegian immigrant who had been a merchant in Crookston before staking his claim in logging country. He coaxed 24-year-old Aagot, a teacher and legal stenographer, to join him on an adjacent parcel.

A neighbor stopping to buy potatoes in early April was the last man to see either Dahl alive. A lumberjack later visiting the Dahl shack found dirty dishes on the table, prompting press reports that they'd left hastily.

When authorities contacted Dahl relatives in Crookston, they made the 100-mile trek east only to discover father and daughter "had disappeared as completely as if the earth had opened and engulfed them," the Minneapolis Journal said, "and there was no satisfactory clue that would explain the mystery."

Detectives from the Twin Cities and the famed Pinkerton agency in Chicago found a button from a woodsman's mackinaw jacket in Aagot's cabin. Relatives joined state and county authorities in offering a $1,750 reward, worth about $51,000 today.

Towering pines weren't the only things casting shadows in the forests near Blackduck. Sketchy characters with prison records frequented the area. "The criminal annals of the state record more murders in proportion to the population in the northern part of the state than in any other section," the Journal reported, under the headline: "DARK CRIME IN NORTHERN WOODS."

Nearly four months after the Dahls' disappearance, a neighbor found the father's decomposed body below the roots of a big balsam tree near his cabin. An autopsy conducted in Bemidji found a bullet wound to his head, while another report said his skull was sliced with an ax.

Three weeks later, on Aug. 17, 1904, another homesteader cutting hay found a human foot under a brush pile and unearthed a skeleton. Clothing at the scene confirmed the remains were those of Aagot Dahl, but the cause of death went undetermined.

The Bemidji Pioneer called it "one of the most cold-blooded and brutal murders" in northern Minnesota history, and the Fargo Forum said Aagot's murder was the "most revolting and diabolical" ever in the state.

Arrests and indictments followed with four men implicated, kicking off a dizzying series of trials, acquittals, convictions and retrials spanning six years. The motive was clear: money.

A few months before he disappeared in 1904, the elder Dahl sold timber rights on his claim for $1,800, worth about $53,000 today. He was rumored to constantly carry large sums of money.

The Bemidji newspaper described Dahl as "an almost helpless old man" and called his daughter "frail and sickly." Their blood was shed "in the hope of obtaining a few paltry dollars, believing that their identity would never be discovered" in such remote and woodsy terrain.

Among the first arrested was Eugene Caldwell, a neighbor who had found Nicholai Dahl's body after reportedly saying he could find the bodies if the reward was large enough.

A grand jury indicted two others with shady pasts, James "Shorty" Wesley and Paul Fournier. Wesley had moved to Beltrami County in 1900 to work as a laborer and lumberjack, and lived with Caldwell. It took a Bemidji jury only 27 minutes in April 1907 to find him guilty of murdering the elder Dahl, and he was sentenced to life in the Stillwater prison.

A laborer from Maine, Fournier moved to Minnesota in 1883 and had done time for robbery before settling in Quiring in 1903. Ten days after Wesley's verdict, Fournier also was found guilty in Nicholai Dahl's death. But he was granted a new trial on grounds of prosecutorial misconduct and a change of venue to Brainerd, Fournier was acquitted of murdering the elder Dahl in 1907, and got the same verdict from an Aitkin jury in Aagot's death after only 23 minutes in 1910 — thanks to attorney Charles Scrutchin, one of the first Black lawyers in the area.

Fournier returned to the woods near Quiring in 1910 to live with cousin George Cyr and his wife. Cyr himself had been arrested in the Dahl murders with Fournier, but charges were dismissed when authorities failed to link him to the crime.

But a couple of years later, according to Cyr, Fournier one day became enraged, confessed to killing the Dahls and rushed at Cyr's wife with a small dagger. Cyr grabbed a gun off the wall and shot him, killing Fournier in what he said was self-defense.

Cyr turned himself in and insisted Fournier participated in the Dahl murders.

"But so far," the Minneapolis Tribune said, "he has not given any particulars nor hinted at anything that is tangible in the way of clearing up the mystery that has surrounded ... one of the most coldblooded and brutal crimes in the history of the state."

Curt Brown's tales about Minnesota's history appear each Sunday. Readers can send him ideas and suggestions at mnhistory@startribune.com.