Juan Corona, a farm labor contractor who was dubbed the “machete murderer” for hacking and killing 25 migrant workers in California — crimes that made him the worst serial murderer in American history at the time of his 1973 conviction — died March 4. He was 85.

The California Department of Corrections and Rehabilitation announced that Mr. Corona died at a hospital outside a state prison in Corcoran where he was serving 25 life sentences. No cause of death was cited, but he was reported to have had dementia.

Mr. Corona’s killings rocked the quiet agricultural town of Yuba City, Calif., a community of 14,000 people about 100 miles northeast of San Francisco, where Mr. Corona, a native of Mexico, lived with his wife and four daughters. His job was to recruit thousands of farm laborers, many of them Mexican, to work in the fields.

The killings were uncovered after a peach grower, Goro Kagehiro, who had hired Mr. Corona to supply field workers, noticed a freshly filled hole about 4 feet deep, 5 feet long and 2 feet wide in his Sutter County orchard on May 19, 1971.

He grew suspicious and called the sheriff’s office. Under the soil was the body of laborer Kenneth Whitacre. Six days later, a second body was discovered in a shallow grave at a nearby ranch, and a third body was found close to the Feather River. Near the third body, a deputy recovered two meat-market receipts bearing the name of Juan V. Corona. After officers unearthed six additional bodies, Mr. Corona, then 37, was arrested on May 26, 1971.

Within a week, the bodies of 25 men had been exhumed. All but one had been slashed in the head with a machete or a knife, and many had been stabbed in the upper body. One victim had been shot. All of the victims had been hired through Mr. Corona’s labor contracting business or had been seen with him.

Notable deaths in 2019: Elijah Cummings, Cokie Roberts, Toni Morrison and others we have lost this year

Don Imus | Don Imus, who spent more than half a century in radio and television skating along the edge of propriety and occasionally falling into the abyss of the unacceptable, died Dec. 27 at a hospital in College Station, Tex. He was 79. In a roller-coaster career in which he grew chummy with prominent politicians, repeatedly got suspended or fired for offensive cracks, abused drugs and touted health foods, Mr. Imus won a loyal following, made millions and transformed himself from a bad-boy DJ into a host whose program became a nearly mandatory stop for presidential candidates. Read the obituary (Richard Drew/AP)

When police searched Mr. Corona’s home and truck, they found a machete with an 18-inch blade, a meat cleaver, a double-bladed ax and a wooden club. There was also a ledger with a list of 34 transient workers, including several of the victims. Despite Mr. Corona’s assertions of innocence, prosecutors called the ledger a “death list.”

Judge Richard E. Patton said during the 1973 trial that he was “truly appalled” and “almost incredulous” at the bumbling prosecution, which was accused of mishandling evidence. “At this point,” Patton said, “it appears the investigation was inept, the preparation inefficient and the prosecution inadequate.”

But extensive circumstantial evidence was presented against Mr. Corona, and he was convicted on 25 counts of murder. A state appellate court overturned his conviction in 1978 on the grounds that his defense attorney had made a “farce and mockery” of the trial and was even more incompetent than the prosecution. No defense witnesses were called during the trial.

Less than a year after entering a state prison in Vaca­ville, Mr. Corona was stabbed 32 times by inmates, lost his left eye and had a blade permanently lodged behind his right eye. He had three heart attacks while incarcerated. His wife, the former Gloria Moreno, divorced him in 1974.

At Mr. Corona’s second trial, in 1982, a different defense team sought to shift the blame to his brother Natividad, who disappeared in Mexico and was thought to be dead. Mr. Corona’s attorney said the brother had “maniacal rage” from “the frustration of a morbid sexuality.”

Mr. Corona testified at his second trial, denying the charges. The jury heard more than 200 witnesses during the seven-month proceedings, which cost the state more than $5 million. The result was the same as the first trial, nine years earlier: Mr. Corona was convicted of all 25 counts of murder.

Juan Vallejo Corona was born in Autlán, Mexico, on Feb. 7, 1934. He moved from Jalisco, Mexico, to Sutter County with two older brothers in the early 1950s. He received psychiatric treatment after reporting that he had seen ghosts.

A complete list of survivors could not be confirmed.

Mr. Corona was the most prolific known mass murderer until John Wayne Gacy Jr. was convicted in 1980 of killing 33 young men and boys and burying most of them beneath his home in Des Plaines, Ill. Gacy was executed in 1994 in Illinois, but Mr. Corona was not subject to the death penalty because California’s capital punishment law had been ruled unconstitutional at the time of his trial.

According to news accounts in 2011, Mr. Corona told a psychiatrist that he killed the men because he believed they were ­“winos” and had been trespassing. Sutter County Assistant District Attorney Jana McClung referenced the admission during the prisoner’s parole hearing that year and noted that Mr. Corona’s descriptions of two victims did not exactly match details about the bodies unearthed in shallow graves in 1971.

“I don’t know if that means there are others out there,” McClung said.