Arnold Diaz, a brash investigative reporter at three New York City television stations who brought righteous passion to segments that shamed con artists, business owners, scammers, government bureaucrats and others who ripped off consumers, died on Oct. 24 in Greenwich, Conn. He was 74.

The cause of the death, at a hospital, was multiple myeloma, a blood cancer, his son, Alex, said.

Mr. Diaz wanted not only to resolve victims’ problems but also to embarrass the malefactors for their misdeeds. He confronted them, chased them and shoved microphones in their faces in search of answers.

At WCBS, Channel 2, where he spent more than 20 years, his “Shame on You” investigations were introduced with a short animation that featured a jingle and a hand with a wagging index finger. When the segment moved to WNYW, Channel 5, it was renamed “Shame, Shame, Shame”; later, on WPIX, Channel 11, it was called “What a Shame!”

“I’ve been lucky to have had a dream job, standing up for the little guy, sticking it to the bad guys,” Mr. Diaz said lon Channel 11 last year, when he retired. He added that his reports “gave voice to victims whose complaints were too often ignored — complaints about lousy landlords, greedy businesses, incompetent government agencies.”

One typical report, from the early 1990s, spoke to people who had bought credit-card-activated fax machines for $5,500 or more that they were told, in a TV commercial, would reap quick profits after being placed in high-traffic locations like airports for public use.

In the segment, the camera zeroed in on the consumers’ losses, the amounts circled in red on their checks. Mr. Diaz clutched paperwork that showed who had purchased the machines; he said that “Shame” had called 34 people on the list and that not one had received the equipment. He tracked down the company, Distribution International, to a “boiler-room” operation in a basement in Forest Hills, Queens, where his questions to Sheri Cohen, the company’s president, went unanswered as he followed her around the office.

When she told Mr. Diaz that some fax machines had been installed, he demanded where, but she refused to answer. And Ms. Cohen, like hundreds of others confronted by Mr. Diaz over the years, was inducted into what Mr. Diaz called his Hall of Shame.

In early 1993, she was charged with wire fraud by the United States attorney for the Eastern District in Brooklyn. Mr. Diaz said the office had credited “Shame on You” for making it aware of the case. Ms. Cohen was convicted one year later and sentenced to 41 months in prison.

Around the time of that report, Walter Goodman, a television critic for The New York Times, praised a series of Mr. Diaz’s investigations.

“Anybody who has ever felt bilked by a car repair outfit,” Mr. Goodman wrote in 1990, “or has wound up with an over-the-hill chicken or been exasperated by the city’s bureaucracy can cry amen to these mini-exposés, which won two New York Emmy Award nominations last month.”

He ended the review: “Hail! Hail! Hail! Hail to you, Arnold Diaz!”

Mr. Diaz acknowledged in an interview with Newsday in 2022 that he didn’t invent the aggressive type of consumer investigation that became his hallmark. But, he said, he took pride in how he adapted it for a New York audience.

“New Yorkers love revenge,” he said, “and, even if I didn’t solve their problems, loved that we exposed” the wrongdoers.

His reporting led to some angry encounters, Alex Diaz said in a phone interview: People would spit and curse at him. In one instance, a Manhattan jeweler, whom Mr. Diaz was investigating for shortweighing gold, menacingly slipped a gun on the table in front of him.

By his count, Mr. Diaz won 48 New York Emmy Awards — so many, his son said, that he lent some to prop houses for use in the backdrops of TV programs.

Arnold Theodore Diaz was born on June 16, 1949, in Brooklyn, and moved with his family to North Miami Beach, Fla., when he was 5. His Cuban American father, Leonard, was an airline mechanic. His mother, Florette (Cohen) Diaz, was a police secretary.

Mr. Diaz graduated with a bachelor’s degree in communications and media studies from Florida State University in 1971 and earned a master’s in journalism the next year from Northwestern University. He soon joined WPLG in Miami, and in 1973 he moved to WCBS, where he stayed for 22 years.

Ann Sorkowitz, a producer who began working with Mr. Diaz at WCBS in 1976, said he distinguished himself on breaking news stories and long-term investigations, such as one on toxic dumping in New Jersey. His investigations generated viewer mail, including consumer complaints. The “Shame on You” reports began in the late 1980s.

“Arnold decided to call it ‘Shame on You’ because of the old-fashioned notion of people practicing bad behavior being shamed publicly,” Ms. Sorkowitz said in a phone interview. “The segments empowered people. They got their problems resolved or got their money back and vented their frustrations.”

Mr. Diaz left local television in 1996 for a network job as a consumer investigative correspondent on ABC’s “20/20.” “I was interested in bringing in that sense of outrage journalism,” Victor Neufeld, the program’s former executive producer, said. “He was the perfect local news person. He was very animated and energized, a crusader.”

But the pace of a network newsmagazine, where it took months for a report to get on the air, “wasn’t his style,” Mr. Neufeld said.

When Mr. Diaz rejoined Channel 2 in early 2003, he told The Daily News in New York: “When you’re in local TV, you think, ‘Oh, if I could only get to the networks.’ I’ve been there. I’ve been to the mountaintop, and the view isn’t any better. Sometimes it’s worse.”

His return to Channel 2 lasted two years. He then moved to Channel 5, where he stayed until 2014, and Channel 11, where he stayed for eight years before retiring.

Alex Diaz attributed his father’s passionate style to his Cuban background and to his upbringing, at least early on, in a working-class Brooklyn neighborhood.

“I was fascinated that he used the power of shame like a weapon or a shield,” said the younger Mr. Diaz, who has the word “shame” tattooed on his abdomen. “Shame is a call for introspection. It was less casting a judgment than saying: ‘You know what you’re doing is wrong. Be a better version of yourself.’”

In addition to his son, Mr. Diaz is survived by his wife, Shawn Callaghan-Diaz, whom he met when she was a set decorator for soap operas and the children’s show “Captain Kangaroo” at CBS; his daughters, Shayna Wade and Casey Diaz; a sister, Susan Enslein; and twin grandsons.

When Mr. Diaz retired last year, he reflected on his reports, including one in which an insurer said it would not pay for a Staten Island man’s prosthetic leg because there was no proof that he wanted to walk. His reporting prompted the company to review the man’s claim and approve it.

“I leave with no regrets,” Mr. Diaz said. “I may miss the excitement but not the times I’ve been shoved, spit at and threatened with guns.”