Note to all police officers in Cambridge, Massachusetts: if you absolutely do have to arrest a black man on suspicion he was breaking into a house that turns out to be his own home then please, please make sure it's not Henry Louis Gates Jr.

To say that the Cambridge force had egg on its face today does a massive injustice to the scale of its embarrassment. One of its sergeants had arrested, handcuffed and banged in a cell for four hours arguably the most highly respected scholar of black history in America.

Prolific writer, television presenter, director of Harvard's WEB Du Bois Institute for African and African American Research, mate of Oprah Winfrey - the list of Gates's connections and accomplishments goes on and on. But when he returned last Thursday to his leafy Harvard home from a trip to China filming his latest TV documentary, he was, well, just another black man engaging in nefarious activities.

It was broad daylight in the early afternoon when Gates, 58, reached his house in a local taxi. The front door had in some way been damaged and he couldn't get in, so he entered through the back door, disabled the alarm, and then again tried to push open the front door with the help of the (black) driver.

A (white) woman walking by saw a black man trying to force the door and leapt to the kind of assumptions that Gates has chronicled over many years.

She called 911, and then hapless Sgt James Crowley turned up at the scene.

By then Gates, settling back home, was on the phone to Harvard's property section to report the faulty door. Crowley asked him to step outside as he was investigating a report of a break-in.

"Why, because I'm a black man in America?" Gates snapped, according to Crowley's police report, refusing to leave his front room.

Asked to prove it was his own home, Gates showed the officer his Harvard ID and local driving license. In return, Gates asked Crowley for his name and badge number.

In his report, Crowley said that Gates accused him of being a racist police officer and told him he had no idea who he was messing with. The officer wrote that when he repeatedly told Gates to step outside, he was met with the response: "Ya, I'll speak with your mama outside."

"I was quite surprised and confused with the behaviour he exhibited toward me," the sergeant said.

Crowley summoned more officers from Cambridge and from Harvard's own police, and Gates was arrested for "loud and tumultuous behaviour".

As news spread of the arrest, friends and colleagues rallied to Gates's side. He was offered the legal help of Charles Ogletree, a Harvard law professor and friend of Barack Obama.

Lawrence Bobo, a Harvard sociologist, rushed to the police station and drove him home after Gates was allowed out on $40 bail. "I felt as if I were in some kind of surreal moment, like The Twilight Zone," Bobo told the Boston Globe. "I was mortified. This is a humiliating thing and a pretty profound violation of the kind of trust we all take for granted."

Within hours of news breaking of the arrest, the Cambridge police had dropped all charges. In a statement, it said that the "regrettable and unfortunate" incident should not be seen as demeaning the character and reputation of Gates nor the character of the police.

Gates gave no further comment. He is fond though of quoting an observation from Bert Williams, an early 20th-century black entertainer: "It's no disgrace to be coloured. But it is awfully inconvenient."