Philadelphia District Attorney Seth Williams' lawyer on Thursday called a new set of fraud charges filed against his client this week "laughable" and questioned prosecutors' motives in seeking to pursue them.

The lawyer, Thomas Burke, said federal authorities had obtained information years ago on Williams' campaign spending and his use of government vehicles that formed the basis of a superseding indictment filed Tuesday.

"Why didn't they charge that in the original indictment?" Burke said. "The only conclusion that I can come to is that they knew they were laughable and unprosecutable. … [But] my guess is they're taking a good look at their original indictment and feel that it's going to be inadequate."

Burke's comments came minutes after a quick court hearing at which his client pleaded not guilty to the eight additional counts of mail and wire fraud.

Assistant U.S. Attorney Robert A. Zauzmer refused to take Burke's bait.

We’ve presented charges that we think are appropriate, and we will address them at trial,” he told reporters.

Williams, 50, said nothing as he left the courthouse on Market Street and was shepherded into a waiting car.

He left just an hour before a key government cooperator in the case against him – Feasterville businessman Mohammad N. Ali, 40 – pleaded guilty to bribery and tax-evasion charges tied to gifts worth thousands of dollars he gave Williams between 2010 and 2015.

"Ali met Williams in 2010 at a Williams fund-raising event," Assistant U.S. Attorney Vineet Gauri said in court Thursday. "Thereafter, they developed what Ali considered a personal relationship."

Ali, who owns businesses selling energy drinks and prepaid cellphone cards, admitted that he bankrolled a 2012 vacation for Williams and a girlfriend to a luxury resort in the Dominican Republic and that he showered him with other gifts including a $3,000 custom-designed sofa and expensive electronics and clothing.

In exchange, Ali told the judge, he sought Williams' help to bypass secondary security screening at Philadelphia International Airport when returning from his frequent trips abroad. He also asked the district attorney to intervene in a drug case against a DJ at the Center City nightspot Rumor, where Ali was a frequent patron.

Ali and his lawyer, Mark Cedrone, declined to discuss the case after the hearing. The businessman's plea came as part of an agreement with prosecutors that could compel his testimony at Williams' trial.

Prosecutors also allege that Williams sold his influence to businessman Michael Weiss, co-owner of the Center City gay bar Woody's, although Weiss has not been charged with a crime.

In addition, investigators say Williams stole $20,000 meant to pay for his mother's nursing home care and misspent more than $10,000 in campaign funds on personal expenses including elaborate birthday dinners, massages, and facials at the Union League and the Sporting Club at the Bellevue.

Williams, who is not seeking re-election in Tuesday's Democratic primary, has vowed to remain in office through the end of his term this year. He agreed in March to a suspension of his law license while he remains under indictment.

He is scheduled for trial May 31, although his lawyer and prosecutors filed a joint motion late Thursday seeking to delay the proceedings until June 19, allowing them more time to file and argue pretrial motions.

U.S. District Judge Paul S. Diamond has not ruled on their request.