Mayer Brown's former chief information officer David Tresch has been arrested and charged with defrauding the firm of at least $850,000 (£537,000) through a series of invoices for work supposedly performed by an unidentified vendor, reports The Am Law Daily.

The US attorney's office in Chicago charged Tresch, who served as Mayer Brown's CIO until June, with one count of mail fraud, according to a statement detailing the charges against him. Tresch is accused of approving payments to the vendor and pocketing "hundreds of thousands of dollars" in illicit proceeds.

Mayer Brown was not identified as Tresch's employer in the complaint filed by prosecutors. The Chicago Tribune first reported news of the charges against Tresch and his affiliation with the firm on Thursday (30 August).

In a statement issued to The Am Law Daily, Mayer Brown confirmed that Tresch worked for the firm until being terminated on 28 June following an internal investigation, the results of which Mayer Brown referred to the US attorney's office in Chicago.

"[Mayer Brown] will continue to cooperate with the US attorney's office in this matter but will have no further comment at this time in deference to the ongoing criminal investigation," the firm said in its statement.

Tresch worked at Mayer Brown in various capacities beginning in May 2004, when he was hired as a server operations manager. He was promoted to CIO in July 2011.

The FBI, which issued its own statement on the case against Tresch, said it has seized approximately $210,000 (£133,000) in bank accounts controlled by the former Mayer Brown employee, as well as a van, camping trailer, and luxury automobile. The FBI further stated that its agents have also obtained the authority to seize a mobile home belonging to Tresch.

The 13-page criminal complaint against Tresch claims that he hired the unnamed vendor in 2004 to provide information technology services for Mayer Brown. According to the complaint, the firm paid the vendor nearly $7.8m (£4.9m) for services rendered between 2004 and 2008.

During that period, more than 95% of the vendor's business came from Mayer Brown, according to information related to the allegations against Tresch released by federal prosecutors and the FBI. Tresch was responsible for reviewing invoices and authorising payments to the vendor for the work its contract employees did for the firm.

Prosecutors claim Tresch received $1.3m (£820,000) from the vendor between February 2005 and March 2011, a sum that represented more than 15% of what it received from Mayer Brown during that same period. Tresch never told the firm about the payments or that he had a financial interest with the vendor, according to prosecutors.

Prosecutors claim that in February 2011 one of Tresch's Mayer Brown superiors told him to stop using the vendor in question. But the vendor continued to submit invoices to Tresch, who allegedly continued to approve payments, despite knowing that the vendor was no longer approved to handle work for Mayer Brown, according to prosecutors.

A status hearing for the charges against Tresch is scheduled for 5 September.

The Am Law Daily is a US affiliate title of Legal Week.