Within days of his arrest on federal corruption charges, former San Francisco Public Works Director Mohammed Nuru began a series of interviews with investigators from the city attorney’s office.

“He spent two days telling all,” said one source familiar with the investigation.

Nuru’s interviews, combined with information the investigators had already dug up, led to 10 subpoenas being issued a few days later.

Subpoenas were served on companies and nonprofits that City Attorney Dennis Herrera believes were involved in funneling donations through charities to help fund city programs and events, such as the Department of Public Works’ Christmas party and Public Works Week, a celebration of the department.

Those subpoenaed include Pacific Gas and Electric Co., builders Webcor, Pankow and Clark Construction; waste hauler Recology; and three nonprofits: Lefty O’Doul’s Foundation for Kids, the San Francisco Parks Alliance and the San Francisco Clean City Coalition.

“We’re following the facts, and we’re following the money. We are going to follow the evidence wherever it leads,” Herrera said in a statement after the first batch of subpoenas was issued Feb. 12.

In addition to identifying city employees or officials involved in potential violations of local law, Herrera said the investigation will also look into contracts, grants and other government decisions possibly “tainted by conflicts of interest.”

“We will get to the bottom of this. San Franciscans deserve no less,” Herrera said in the statement.

Gaining Nuru’s cooperation was a key reason city officials resisted calls for his immediate firing after federal prosecutors announced his arrest on charges of corruption and fraud.

The charges involve an alleged scheme by Nuru and a friend, restaurateur Nick Bovis, to bribe an airport commissioner with $5,000 cash to help Bovis and two other men, who turned out to be FBI undercover informants, to win a restaurant lease at San Francisco International Airport.

They never actually offered the bribe, but the FBI sources caught the conversations on tape.

Other schemes alleged by the feds but not charged included Nuru supplying Bovis inside information on a city contract for portable toilets and Nuru accepting improper travel and lodging gifts from a Chinese developer who was seeking help resolving a problem he had at the Department of Building Inspection.

Nuru also allegedly had city contractors do work on his vacation home in Colusa County. The feds also alleged that Nuru used city money to reimburse Bovis for “free meals” at Bovis’ Fisherman’s Wharf restaurant for Public Works employees assigned to work holidays.

When confronted with the allegations and evidence, Nuru agreed to cooperate with the FBI as part of its investigation into corruption at City Hall.

Within days, however, he violated the agreement to keep mum about his cooperation and called his boss, City Administrator Naomi Kelly, telling her the FBI was looking at Public Works.

After informing Mayor London Breed and Herrera, Kelly contacted federal officials. As a result, Nuru was rearrested for breaking his cooperation agreement and now faces up to 20 years in federal prison for bribery, conspiracy and breaking the agreement to stay mum about the investigation.

Shortly after Nuru’s arrest, the city attorney called him for questioning. Those interviews were conducted while Nuru was still on the payroll.

“As long as Mohammed was working for the city, he was compelled to come in and answer questions,” the source said. “He has to answer them all. He can’t take the Fifth.”

At the same time, whatever Nuru told city investigators went under seal and cannot be used against him in a criminal prosecution.

Coming clean and showing a willingness to cooperate with the local investigation may also help Nuru with the judge when it comes to sentencing on the federal charges if he is convicted.

“He was told to be at the city attorney’s office at 10 in the morning, and he was there at 9:45 with his lawyer and ready to go,” one source said. “He was in for two and possibly three separate interviews.”

Herrera’s office is mum on what transpired.

“This investigation is ongoing, and we’re not going to comment beyond our earlier public statements,” city attorney spokesman John Coté said.

Where the investigation goes from here remains to be seen, but sources say some people at the Department of Building Inspection should be nervous as well and may be asked to sit down with city investigators in the coming weeks.

“It’s all about pulling the string and seeing what unfolds,” the source said.

Gift fallout: Mayor London Breed’s admission that she accepted $5,600 in assistance from then-Public Works Director Mohammed Nuru was a major lapse in judgment and probably a violation of city rules barring the acceptance of gifts from subordinates as well.

But it won’t result in her being removed from office.

“There is an ethical violation, and I think the Ethics Commission could move on that, but I don’t see any kind of criminal violation,” former Ethics Commission President Peter Keane said.

Breed is in hot water for having Nuru — whom she once dated — take care of repairing her car last year and providing her with a rental car while the work was being done.

In most cases, a fine issued by the city Ethics Commission or the state Fair Political Practices Commission for such a violation is three times the amount in question. So Breed’s decision to let Nuru put up the $5,600 would cost her about $16,800.

But given the local commission’s track record, it will also take months — or even years — before a final determination is made.

“Although with something this high profile, I would think there would be pressure to move faster,” Keane said.

Whatever the two commissions might decide, it won’t lead to Breed’s removal from office.

“I don’t think it rises to that level,” Keane said.

Besides, under the City Charter, the only person who can remove or suspend a local official from office is the mayor. And chances are Breed isn’t going to remove herself.

The only way to remove a mayor is by voter recall.

San Francisco Chronicle columnist Phil Matier appears Sundays and Wednesdays. Matier can be seen on the KGO-TV morning and evening news and can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415-777-8815, or email pmatier@sfchronicle.com. Twitter: @philmatier