David Tresch, who until June served as Mayer Brown‘s chief information officer, was arrested Thursday and charged by federal prosecutors in Chicago with defrauding the Am Law 100 firm of at least $850,000 through a series of phony invoices for work supposedly performed by an unidentified vendor.

The U.S. attorney’s office in Chicago charged Tresch with one count of mail fraud, according to a statement detailing the charges against him. Tresch, 51, 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 Thursday afternoon.

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

“[Mayer Brown] will continue to cooperate with the U.S. 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.

The Federal Bureau of Investigation, which issued its own statement on the case against Tresch, said it has seized approximately $210,000 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—which has since moved its operations to the northwestern Chicago suburb of Schaumburg—nearly $7.8 million for services rendered between 2004 and 2008.

During that period, more than 95 percent 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 authorizing payments to the vendor for the work its contract employees did for the firm. Prosecutors claim Tresch received $1.3 million from the vendor between February 2005 and March 2011, a sum that represented more than 15 percent 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.

Between May 2011 and May 2012, Mayer Brown issued checks totaling $980,000 to reimburse the vendor, which had ceased providing services for the firm after March 2011. Prosecutors claim that during that same time period, the vendor issued 11 checks to Tresch totaling $854,250 that he deposited into one of two personal bank accounts he controlled. The funds in question were then allegedly used to make payments on the camper, mobile home, and vehicles that the FBI has seized.

The $854,250 allegedly paid by the vendor to Tresch between May 2011 and May 2012 represents nearly 90 percent of the $980,000 that Mayer Brown paid to reimbursed the vendor, according to the criminal complaint against Tresch.

Kent Carlson, a solo practitioner in Chicago representing Tresch, did not immediately respond to a request for comment on the charges against his client.

Tresch’s LinkedIn profile says he 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. His employment history was confirmed in background materials released by prosecutors after the criminal complaint against him was filed and unsealed Thursday.

Tresch isn’t the only high-ranking staffer at an Am Law 100 firm to run afoul of the law in recent years.

In 2009, Wilson Sonsini Goodrich & Rosati was the victim of a $1 million office supply scam involving former purchasing specialist John Masakazu Tashiro and two other individuals not affiliated with the firm. Tashiro pleaded guilty the following year to money laundering and mail and wire fraud charges.

In 2010, Jeffrey Temple, a former information systems and security manager at Delaware firm Richards, Layton & Finger, was charged with securities fraud by federal prosecutors after the SEC accused him of engaging in insider trading. Temple, who was alleged to have committed such acts through his position at the firm, pleaded guilty to one count of securities fraud in March 2011.

As for Tresch, prosecutors identify him as a resident of Itasca, Illinois, which BusinessWeek ranked in 2009 as the best affordable suburb in the state.

Terra Reynolds, an assistant U.S. attorney in Chicago, is prosecuting the case against Tresch, who has been released on a $100,000 partially secured bond after appearing before U.S. Magistrate Judge Sidney Schenkier, a former partner at Jenner & Block.

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