There is an internal affairs investigation of Cambridge Police Sgt. James Crowley under way, a department spokesman has confirmed.

“I can confirm that there is an active Professional Standards investigation into alleged misconduct on the part of Sergeant Crowley and, as the investigation is still ongoing, we aren’t going to be making any further comment on specific aspects of the investigation,” communications specialist Dan Riviello said in a Tuesday e-mail.

The bulk of the allegations against Crowley involve a personal matter, according to documents received by Cambridge Day.

Cambridge Day isn’t repeating the allegations, but some of Crowley’s behavior as outlined in the complaint, if found to be true, would violate police procedure, according to an expert on Cambridge police matters who insisted on speaking off the record.

The charges are not linked to Crowley’s July 16, 2009, arrest of Harvard professor Henry Louis Gates Jr.

That arrest set off a firestorm in Cambridge and around the world, initially because Gates is black and Crowley is white, and resulted in radical changes in city police procedure and a nine-month, $241,360 committee that produced a 60-page report suggesting further changes. At first, Police Commissioner Robert Haas said Crowley’s actions had been in line with his training and national standards, but Haas later said the arrest, for which charges were dropped, was “an aberration that does not reflect how the Police Department sees itself or generally does its job.”

Crowley was lauded throughout the Gates affair as a decorated, trustworthy officer with a solid record — a Cambridge native who grew up amid diversity and even taught fellow officers how to stay clear of charges of racial profiling. In January he was invited to speak at the Randolph Regional Police Training Academy cadet graduation ceremony, although state officials vetoed the choice.

Police documents requested by Cambridge Day show there was minimal investigation into Crowley’s arrest of Gates. Over less than a week, police spoke with five people, only one of whom had seen the arrest, before Haas decided — without setting anything down on paper or in an e-mail, according to Kelly A. Downes, legal adviser to the department — that there was no need for a Professional Standards investigation.

Professional Standards can launch an investigation without a complaint, although there is one in the current case. Haas’ rejection of an investigation in the Gates case suggests he or other Cambridge police officials find enough merit in the current accusations to make a probe worthwhile.

Still, the department was reluctant to investigate, according to Crowley’s accuser, possibly because of the personal nature of most of the allegations. The accuser said Friday that he tried to get police to look at Crowley’s behavior two months ago, but sent material to city officials last month when police didn’t respond.

“I was frustrated … initially they weren’t willing to look at any of it, they said nothing was actionable,” the accuser said. “The only reason they decided to take it up is because I sent everything to City Hall.”

Professional Standards “conducts an independent investigation by speaking with the complainant and any officers or relevant parties involved. The average case takes 30 to 60 days to complete, depending on the complexity of the case and availability of witnesses. Once the investigation is concluded, a detective in the Professional Standards Unit will notify the complainant by mail of the findings,” a police spokeswoman said in March.

The accuser said he supplied materials to police that could help in their investigation but had not heard back until late Friday afternoon.

An attempt to reach Crowley for comment while off-duty was stymied by his unlisted telephone number.