Special Counsel Robert Mueller has spent $3.2 million on his investigation since he was appointed in mid-May.

His office announced another $3.5 million has been spent separately on the investigation by the Justice Department in support of the special counsel's office, which is looking into Russian interference in the 2016 election and possible collusion with the Trump campaign.

The expense report, which describes spending through Sept. 30, says roughly $1.7 million was spent on salary and benefits — the priciest expense. There are at least 16 attorneys working on the probe.

Another $730,000 was spent on buying property and equipment, and $362,000 on rent, communications, and utilities.

According to a spokesperson for the office, the next expense report will be released after March 31, 2018. The Justice Department’s Justice Management Division reviews the special counsel’s expenditures every six months.

The investigation has resulted in charges against four people: former Trump campaign chairman Paul Manafort and his business partner Rick Gates, former national security adviser Michael Flynn and former foreign policy campaign adviser George Papadopoulos.

Senate Judiciary Committee Ranking Member Dianne Feinstein, D-Calif., praised the budget as "reasonable."

The expenditures are "entirely reasonable given the results we've already seen. [...] It's clear the investigation is moving forward," Feinstein said in a statement, adding she will continue to support Mueller and his team.