“America’s Most Wanted” co-host Callahan Walsh says investigators are up against steep challenges in the Brown University shooting case as the search for the gunman enters a fourth day.

“The fact that there’s very little information is very concerning,” Walsh said Tuesday, pointing to a shortage of evidence on “Fox & Friends.”

Authorities released video of the suspect, believed to be about 5 feet, 8 inches tall with a stocky build and dressed in dark clothing, but Walsh said the footage offers almost nothing for the public to work with.

“There’s a lot of people that match that description, unfortunately,” he said, adding that the grainy video is unlikely to generate an identification from anyone who doesn’t already know the suspect personally.

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Walsh also touched on that point Monday on “Jesse Watters Primetime,” noting that the suspect’s face is covered, and no distinguishing features are visible in the footage.

On Tuesday, he added that the scarcity of usable surveillance footage is especially striking because the campus is equipped with hundreds of cameras.

“[With] over 800 cameras on that campus and hardly one shot of this individual, it’s astonishing. It’s really mind-blowing,” he said.

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“That’s why I believe the guy does have a serious connection to the school. He knew where he was going. He knew what he was doing.”

Walsh’s comments came after a person of interest detained in connection with the attack was cleared and released. He said that development poses another setback, forcing law enforcement to “restart” the investigation.

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“That is so much time lost…” he lamented.

“They’re going to have to go back and re-interview all the eyewitnesses there and try to figure out, was there anything that they missed? Is there something additional that they can provide now that they have this footage? Can they put this together… and make sure, ‘Is this guy in this footage actually the shooter or not?’ We also need to know what he said in that classroom…. I think that’s going to be very important as well.”