You’ve probably heard the basic story: A black professor at Columbia University found a four-foot noose hung on her office door Tuesday. Pretty soon, the US Department of Justice started investigating.

The DOJ joins the New York City Police Department hate crimes task force in trying to determine who could have hung the 4-foot-long hangman’s rope on the doorknob of Madonna Constantine, a professor at the university’s graduate education school.

“The Department of Justice — including the FBI, the U.S. Attorney’s Office and the Civil Rights Division — has opened an investigation into this matter, and we will coordinate with the New York Police Department hate crimes task force, which is already investigating,” a source within the DOJ told FOXNews.com in an e-mail.

The noose was discovered Tuesday by one of Constantine’s colleagues. A police official told The Associated Press that investigators were looking at whether a fellow faculty member at Teachers College with whom Constantine had a dispute or an unhappy student might have been responsible.

Detectives were testing the twine noose for DNA evidence, according to Deputy Inspector Michael Osgood, commander of the NYPD hate crimes division.

There has been a rally on campus denouncing the noose, with signs comparing it all to Jena, LA and so forth. And the police are pursuing one lead involving the possibility that a fellow professor with whom Constantine has had an ongoing feud could have placed the noose.

But now there’s a curious development. Columbia has a surveillance video that ought to show who put the noose on the professor’s door. But the university isn’t releasing it to the police.

Columbia University has refused to turn over security videotape that could help identify who hung a noose on a black professor’s office door, police said Thursday.

Investigators began asking on Wednesday for tapes from cameras in the building, but have been rebuffed by administrators, said Paul Browne, the New York Police Department’s top spokesman.

He said police will have to get a court order to force the school to provide video they believe could crack the case.

“It’s unfortunate because it adds a time-consuming step to the investigation,” Browne said.

That’s odd behavior, all things considered. If the perp is on the tape, and the university has the tape and wants the police to find the perp, you’d think that the university would hand over the tape. And if the perp isn’t on the tape, hand it over anyway so the police can rule that line of evidence out as quickly as possible. To not hand over the tape is, potentially, to protect a racist who is threatening one of the university’s professors.

Columbia president Lee Bollinger has already gone on record that the noose incident is horrible:

“This is an assault on African-Americans and therefore it is an assault on every one of us,” Columbia president Lee Bollinger said in a separate statement. “I know I speak on behalf of every member of our communities in condemning this horrible action.”

It is indeed an assault, and whoever did it ought to be found out and punished. So why not turn over the tape and help police get to the bottom of all this as soon as possible?

Update: CU flip-flopped and is handing over the tapes. And now there’s been an incident of anti-Semitic graffiti on campus, too.