Harold Weisberg, a prolific author and persistent critic of the official report that found a lone gunman responsible for the death of President John F. Kennedy and who was often dubbed the dean of assassination researchers, died Feb. 21 at his home in Frederick, Md. He was 88.

He had a kidney ailment and sepsis.

Weisberg’s career as the writer of about 10 published and roughly 35 unpublished books on the murders of Kennedy and the Rev. Martin Luther King Jr. came last in a series of endeavors. He had been a journalist, a labor investigator for then-Progressive Party Sen. Robert M. La Follette Jr. of Wisconsin, an investigator for a World War II spy agency, a State Department intelligence analyst and a prize-winning Montgomery County, Md., poultry farmer.

In an obsession that kept him in financial hardship during the last 35 years, Weisberg collected in his home more than 250,000 government papers on the 1963 Kennedy assassination and scoured millions more at the National Archives. He produced one of the earliest books about the president’s death, in 1965 called “Whitewash.”

Weisberg also became a leading authority on the 1968 King killing and was an investigator on behalf of the late James Earl Ray, who pleaded guilty to the crime but later recanted.

Weisberg came to believe neither Lee Harvey Oswald, the accused Kennedy gunman, nor Ray, were responsible for the deaths of the prominent leaders. He focused on what he considered the inadequacies of the government investigations, specifically an improper probe of the available evidence. But for all his work, he never found a definitive answer.

He detested many other students of conspiracy, foremost filmmaker Oliver Stone, whose 1991 “JFK” spun out all kinds of theories about the president’s death.

“To do a mishmash like this is out of love for the victim and respect for history?” Weisberg said to The Washington Post. “I think people who sell sex have more principle.”

In contrast, Weisberg presented information he gleaned from government investigative papers in an often dry manner even if that belied his cover tag lines promising “the end of the cover-up official lies exposed. Never such an investigation never such evidence!”

Weisberg, friends said, had a photographic memory, and a single-minded focus on his work that kept him occupied seven days a week. He once told The Post that he worried he would be judged long after his death as “a goddamn fool or Don Quixote.”