Television can be a cruel medium, especially when you’re forced to do it without pictures. Such was the case Monday with NBC’s “Rock Center,” which scored a journalistic coup: Bob Costas‘ interview with Jerry Sandusky, the alleged child molester at the center of the scandal that has rocked Penn State and led to the firing of its legendary coach, Joe Paterno.

Except Costas had to conduct the interview over the phone, which deprived us of many of the cues we’re accustomed to when watching a TV interview: Body language, physical bearing, the look of the person, allowing us to conduct our own version of a visual lie-detector test.

To his credit, Costas asked all the right questions — fairly, but with an understandable tone of righteous indignation.

The answers were also telling. Sandusky admitted that he had “horsed around with kids,” but “without intent of sexual contact.”

For the most part, it was a blanket denial, in the face of a tremendous amount of evidence, including eyewitness testimony. Each time Costas asked about why someone would lie about having seen him having sex with children, Sandusky replied with some variation of “You’d have to ask them.”

Still, NBC didn’t do all with the piece that it could have. Costas had Sandusky’s attorney in the studio, but asked him only a few questions. Pressing the lawyer in person at least would have at least provided a more traditional TV news experience.

It’s telling, too, that the rest of the hour was again rather flat. Yes, there was a solid story about Alabama’s anti-immigration law, but a rather limp interview by Kate Snow with the state’s governor. And Williams’ banter with the correspondents feels increasingly stilted — as if he’s trying to beat us over the head with how impressed we should be with the reporting.

Ultimately, for all its aspirations to do serious broadcast journalism — if that isn’t often an oxymoron — “Rock Center” frequently comes across as too precious for its own good. (That included a self-congratulatory plug for NBC hiring Chelsea Clinton, which — like most celebrity hires — is more about grabbing attention than journalism.

The shame would be if people derive the wrong message from the “Rock Center” experiment. If the show continues along this path, it won’t fail because it’s serious. It will fail because it’s another mediocre hour on a struggling network. And as much as NBC News would like to blame that on the network’s primetime woes, it will have mostly itself to blame.