Capitol Police ramped up their investigation Wednesday into a series of small, suspicious fires that have burned in women’s restrooms located throughout Senate office buildings over the past several days.

The four fires that burned in restroom trash cans in the Dirksen and Hart buildings from mid-morning to mid-afternoon on Wednesday followed two similar blazes in the Hart Building last week.

All were quickly extinguished by police and no injuries were reported, Capitol Police spokeswoman Sgt. Kimberly Schneider said.

Three of the fires set Wednesday took place in women’s restrooms in the Dirksen Building, while one took place in Hart. The Sept. 26 and 28 fires were similar to Wednesday’s, as they took place in women’s restrooms and were quickly extinguished by Capitol Police, Schneider said.

It is unclear who is behind the fires and why they have been set, but the department is actively trying to find those answers, Schneider said.

“We’re working on it. We’re investigating,” Schneider said.

The department also turned to Congressional staff for help in the investigation Wednesday afternoon, as the Office of the Senate Sergeant-at-Arms sent out an e-mail alert to Senate staff informing them of the fires and asking for assistance.

“Capitol Police have added additional building patrols in the office buildings and the matter is under investigation by the Criminal Investigations Section,” the e-mail reads. “Any staff members who have witnessed any unusual activity or behaviors that may be associated with these fires are requested to contact the U.S. Capitol Police Command Center.”

Sergeant-at-Arms Terrance Gainer said Wednesday that while most of the investigation and response to the fires falls to the Capitol Police, his office remains in touch with the department to ensure there is no larger terrorist threat.

“There doesn’t appear to be that,” added Gainer, a former Capitol Police chief.

Gainer and his staff also are charged with informing the Senate community of incidents on Capitol Hill. The decision to send out the e-mail alert was made Wednesday as a way to let Senate staff know what was going on, keep things calm and possibly drum up leads, Gainer said.

Investigating the incidents is tricky because restrooms are by nature somewhat private. Plus, it is difficult to detect someone quietly lighting a match and throwing it into a trash can, Gainer said.

At the same time, there are effective ways to investigate, Gainer added. The department and other security officials likely will work with the Bureau of Alcohol, Tobacco and Firearms to look at police surveillance tape and determine if a pattern can be established.

“Anytime you have four incidents in one week, you have to be on guard,” Gainer said. “You don’t want a wholesale fire over there. But I don’t think we should push the panic button yet.”

Sen. Mary Landrieu (D-La.), who has oversight of the Capitol Police as chairwoman of the Appropriations Subcommittee on the Legislative Branch, is confident the department will solve the case, a spokeswoman said.

“The Senator has every faith that the Capitol Police will be able to investigate these incidents thoroughly and get to the bottom of it,” spokeswoman Stephanie Allen said.

The Dirksen Building has been the site of multiple incidents this week.

On Monday, a staffer alerted Capitol Police to a man who allegedly was throwing bricks at the building’s windows, managing to break two of them.

Police arrested Washington, D.C., resident Ross Gardner Lee, 44, at the scene. He since has been charged with destruction of property.