OAKLAND — About 25 special agents with the ATF’s National Response Team were on the ground Thursday combing the site of Monday morning’s five-alarm fire at an apartment building under construction.

The Bureau of Alcohol, Tobacco, Firearms and Explosives brought tools and gear — a pair of accelerant-detection K-9s to find the cause of the blaze of the structure in the 300 block of Lester Avenue.

“Our highly experienced investigators conduct thorough and methodical investigations based on the scientific method,” ATF Assistant Special Agent in Charge Debbie Livingston said in a statement late Wednesday. “They approach all scenes with an open mind and no preconceptions. The NRT’s presence here is investigative in nature to support Oakland Fire Department.”

“Our housing is critical, and we can’t afford to lose any of it. If this was suspicious or accidental, we need to know in order to prevent this from happening again,” Oakland fire Chief Teresa Deloach Reed said Thursday evening in a separate statement. “The NRT has the resources to conduct such an investigation.”

The team began work with hired contractors to clear remnants of scaffolding looming over the site’s scorched walls, including some still perilously tipped against at least one neighboring building, ATF spokeswoman Lisa Maiman said Thursday.

Once the scaffolding is gone, agents can begin combing broader areas of the property beyond the limited area already assessed by the K-9s for signs of a cause.

Some team members fanned out to knock on doors, introduce themselves and collect eyewitness accounts and other evidence. Agents have spoken with security staff on site, and have been in contact with the Magganas family that owns the property, Maiman said.

“We’ve had agents talk to a lot of the neighbors after they came home from work,” Maiman said. “We’ve asked for photos and videos, and the community has been great in providing those.”

Maiman said agents were grateful for the hospitality and understanding they had encountered so far.

“We’ll be working really hard to complete the on-scene investigation as expeditiously as possible,” Maiman said. “We don’t stop for weekends.”

The fire broke out about 5:07 a.m. Monday at the 41-unit five-story apartment complex. It threatened several other buildings, forcing fire crews to evacuate between 100 and 200 people.

A security guard and his girlfriend were staying on the property when the fire began. The girlfriend was treated for an anxiety attack, but there were no other serious injuries.

Damage was estimated at $1 million.

Maiman said ATF agents are seeking a comprehensive collection of clues as possible evidence and that includes searching social media.

The team’s aim is to create a timeline that offers insight investigators can use and offer a report to Oakland fire officials within 30 days, she said.

The property owners did not return calls for comment from this newspaper.

In an unrelated fire, Emeryville police said Thursday they are still investigating the cause of a July 6 six-alarm blaze that roared through a five-story townhome under construction in the 3800 block of San Pablo Avenue and took nearly five hours to control.

As with the Oakland fire Monday, no injuries were reported, but dozens were evacuated when heat and embers threatened nearby occupied housing. No cause or suspect information was available, but the department is working closely with the ATF’s National Response Team, Emeryville police Sgt. Fred Dauer said

“Anyone with information, we’d love to hear from them,” said Dauer, who spoke with the case’s lead detective Wednesday.

Anyone with information on the Emeryville fire should call police at 510-596-3700, with calls remaining anonymous upon request.

Contact George Kelly at 408-859-5180.