“Prime Suspect” (NBC, 9 p.m.) winds up its unsuccessful season by showing its final two episodes before the hat is retired for good. Network chief Robert Greenblatt told TV critics said that it didn’t gain enough viewers in short enough time since its fall debut.

“Ten or 15 years ago, you could keep a show on the air and slowly over time build an audience,  but we do have a lot of evidence that a modern audience, if you don’t get them within the first four or five episodes, it’s really hard to get beyond that,” Greenblatt said. “I spent several weeks in the Fall trying to get trying to build an audience for ‘Prime Suspect,’ and we did a number of different things to find that audience and just came to the conclusion that was a painful one that we were never going to find a way to grow that audience.”

At Showtime, which he ran for several years, “Prime Suspect” would have been picked up in the third episode, declared a hit and would have likely been in production for four or five years.

“But when you look at each show, and look at what it cost to make it versus what the ratings are versus what the advertising revenue is for that time period, you can’t be as cavalier about, ‘Oh, we love the show. We’re just going to keep it on for as long as we want.’

Greenblatt called “Prime Suspect” his biggest disappointment at NBC so far.

“Creatively, I really loved that show, and I think everybody who worked on it really delivered,” he said. “And I think Maria Bello was incredible.”

But he said, you can’t spend $20 million on an ad campaign. “The show has got to do some of the heavy lifting.”

And what was it that went wrong?

“We talk a lot about, “Is that too ‘cable’ a character for the broadcast audience? Is she too abrasive?” Greenblatt said. “It’s hard to ever know. The audience seems to want to be entertained with escapist and fantasy, and they love comedy, and they love fairy tales now. So maybe a hard hitting cop show with a dead body in the first scene wasn’t the appetite of the country.”

Or, he added at last, “Maybe I should just blame the hat and move on.”