Cambridge’s Police Review and Advisory Board has completed its preliminary investigation into last summer’s arrest of Harvard professor Henry Louis Gates Jr., but the board’s executive secretary clarified Thursday that it’s the word “preliminary” that’s significant.

“As the release said, it was a preliminary investigation, so the board is still gathering information,” said the board’s executive secretary, Marlissa Briggett, referring to a press release dated April 28 that can be read on the board’s website. “They just wanted to let people know that they are working on it. They will be coming out with some recommendations [for police]. I can’t give you a specific date on that.”

The status update was given because the board was being asked about progress, Briggett said. In the past, board members had expressed frustration with the difficulties of pursuing an investigation without the cooperation of the people involved.

The investigation is looking into the July 16 arrest of Gates by Cambridge Police Sgt. James Crowley. Crowley was at Gates’ home in response to a report of a possible burglary, but arrested Gates on a charge of disorderly conduct after the burglary fears were resolved. The professor had accused Crowley of being there because of his race — black, while Crowley is white, and the incident gained international prominence after President Barack Obama, a friend of Gates’, said police had “acted stupidly.”

The citizen-run police oversight board is acting based on complaints from “non-involved third parties,” not from Gates or anyone else involved in the incident, and not by the request of the city. Instead, in September City Manager Robert W. Healy and Police Commissioner Robert Haas formed a separate, $210,000 committee to look at issues surrounding the Gates incident, although not at the Gates incident itself, and filled it with about a dozen people from around the country.

That panel, called the Cambridge Review Committee, “hopes to produce its final report in the late spring,” according to a March 1 progress report issued by committee liaison Jennifer Flagg.

Early this spring the committee invited PRAB to its April 26 meeting, and Briggett said that gathering of the two panels took place.

“It was really nothing, just an introduction of PRAB to the committee, that kind of thing,” she said. “Really nothing to speak of.”

That introduction may have taken place as the committee winds up its work.

When the 12-member panel was created in September, Haas said it was working on a timeline of about five months, but that deadline was extended. In mid-January, the Cambridge Chronicle reported that the committee was saying a final report would be made public some time in the “early part of 2010.”

From attending the April 26 meeting, Briggett got the impression the committee was “hoping it’s going to be soon, but there’s no firm date” on a final report release date.

Messages were left with Flagg on Thursday evening.

In other board news, a fifth and final volunteer member has been appointed: Alexandra Detjens, violence prevention coordinator of the Cambridge Public Health Department. Her seat had been empty some 16 months, and Briggett (who started about three months ago) filled a seat that had been empty for about a year, but with Detjens’ appointment the board is back at full staff.

Healy moved quickly since getting the board’s nomination last month. In the past, board members have said, the city manager has taken up to a year to confirm a nomination.