The co-host of Jill Dando, Crimewatch, says the police had a "scattered approach" and a "silly vision" that their murder was related to the program.
Nick Ross said the detectives focused on the wrong lines of investigation during the weeks after the BBC host was shot dead outside London in April 1999.
Speaking at the Daily Mirror, he said he believed that the murder was not related to his work to help bring criminals to the television show.
"The thing is, and not so much the fault of the senior research officer, but the best, had this intuition and, we thought, a rather dumb view, would be related to Crimewatch," said the young man of 71 years. .
"In modern times, there has never been an attacked judge to send someone, a lawyer or any other person. It's just not like happening here …
"Many of the appeals could be frustrating when the police had this dispersion approach."
Barry George was found guilty of the murder of Dando and spent eight years in prison before he was acquitted in a new trial in 2008.
Ross also criticized the police for placing too much emphasis on a captured CCTV vehicle near the assassination scene.
"The police were still asking for testimonials of a Range Rover," he told the Daily Mirror.
"The Range Rover had at that time a particular association with crime.
"But they were looking for a lot of things that probably had a lot of people called, but that was not very concentrated."
Ross said the police ended up "worsening" with more than 7,000 research lines.
Twenty years after his death, he also paid homage to Dando, describing her as "a person so generous, pleasant and affected."
The investigation into the 37-year-old murder opens, and the Met police are said to investigate any new information that is available.