The law firm hired by the Christie administration to investigate last year's lane closures at the George Washington Bridge has billed the state more than $7.2 million through July, invoices released late Friday afternoon show.

Gibson Dunn & Crutcher L.L.P. billed the governor's office $784,459.10 from May through July. The bills cover the firm's internal investigation into the administration's role in the bridge scandal, as well as legal assistance in responding to subpoenas. Taxpayers are covering all the costs, at $350 an hour.

Gov. Christie's office hired Gibson Dunn in January after e-mails subpoenaed by legislators showed the apparent involvement of one of his top aides in the lane closures, which snarled traffic on the bridge for four days last September.

Christie fired the aide, deputy chief of staff Bridget Anne Kelly, and cut ties with his former campaign manager, Bill Stepien, as well after his name surfaced in the documents.

Gibson Dunn released a 360-page report in March that pinned blame for the traffic jams on Kelly and former Port Authority official David Wildstein, another former Christie ally. The report concluded that Christie did nothing wrong, and he has maintained he was not involved.

The U.S. Attorney's Office has said it is investigating the matter, as is a special legislative committee.

The legislative panel's outside counsel had submitted invoices totaling more than $700,000 through March, also to be picked up by taxpayers.

Gibson Dunn billed the state $388,014 in May; $249,972.40 in June; and $146,472.70 in July, according to the invoices released Friday.

The governor's office also is covering the legal bills of several current and former staffers who have received subpoenas related to the lane closures. Those bills have totaled more than $670,000, according to invoices, which edit out the employees' names.

Gibson Dunn's invoices list items such as "work on investigation-related issues" and "review documents for production to" the legislative committee. Clients' names and other details are also redacted.