Joshua M. Peck, a spokesman for Duane Morris, said Mustokoff would have no comment.
Commissioner Rick Taylor, who is also a Pennsauken committeeman, participated in the meeting by telephone. Taylor said the group discussed the federal inquiry, e-mails that were supposed to be preserved for federal investigators but were not, and other topics that included the need for board members to communicate clearly among themselves.
"We covered so much in those two hours," Taylor said. "People said what they wanted to say."
The U.S. Attorney's Office in Philadelphia has been investigating the DRPA for more than a year, focusing on the agency's past economic-development spending, in which nearly $500 million was spent on sports stadiums, museums, concert halls, and other projects unrelated to transportation.
In attendance at Duane Morris' Center City office were Jeffrey L. Nash, the Camden County freeholder who is vice chair of the DRPA board, and John "Johnny Doc" Dougherty, the Philadelphia labor leader who is the board designee of Pennsylvania Auditor General Eugene DePasquale.
Listening in by speakerphone, in addition to Taylor, were Pennsylvania Lt. Gov. Jim Cawley, chairman of the DRPA board, and DePasquale, who heads the board's audit committee.
Hanson, the DRPA's two top lawyers, and Cawley's chief of staff also participated. A spokesman for Cawley said the lieutenant governor was "out of pocket" and unable to respond to questions about the meeting. He referred calls to Hanson.
The meeting was held in response to a request made several weeks ago by Dougherty, who asked Cawley to convene an "emergency" board meeting after the board was told that internal e-mails requested by federal investigators had apparently been lost despite orders to preserve them.
"All of the facts need to be presented to and discussed among the entire board in an open and transparent manner," Dougherty said in his letter to Cawley last month. "To do anything less is to invite further scrutiny from law enforcement agencies and lend credence to the growing speculation that certain former and/or current DRPA officials may have obstructed justice."
Dougherty did not return calls seeking comment on the unpublicized meeting. In a statement issued by a spokesman, he said: "Since my original tenure on the DRPA board and continuing today, I have always advocated for greater transparency and access for the public.
"Yesterday's meeting was about establishing those parameters and working cooperatively towards more accessible and transparent operations at the authority. Auditor General DePasquale and I appreciated the board's responsiveness to our concerns."
DRPA officials said in June that the loss of the e-mails was inadvertent and blamed faulty software. Taylor said Thursday that those participating in Wednesday's meeting had been assured during the briefing that a "glitch" erased the e-mails and that it would not happen again. Taylor was unsure whether the e-mails that were lost could be recovered.
The e-mails were among communications and documents that federal investigators in March 2013 instructed the DRPA to preserve.
Wednesday afternoon's meeting lasted about two hours, Hanson said. He declined to detail what was discussed.
DePasquale confirmed Thursday that he participated in the meeting by phone. He expressed concern that DRPA officials had not advised the public that board members were meeting in executive session to discuss a legal matter.
"These meetings should be posted," he said. He said the public should have been told of the meeting, its purpose, and the time and place it was to be held, even though it was an executive session and could legally be held in private.
In the future, DePasquale said, "We are going to make a point whenever we have one of these things, to make sure that they are posted."
Nash, who also attended the meeting, said that since the gathering was not a board or committee meeting and there was no quorum, there was no requirement to inform the public.
"It was a meeting to discuss a legal matter," Nash said. "And that's all I am going to say about it."
Because the DRPA is a bistate agency with representatives from both Pennsylvania and New Jersey, it is not necessarily subject to open meeting laws in either state, said Walter M. Luers of the New Jersey Foundation for Open Government.
To enforce such laws on a bistate authority, Luers said, legislatures in both states would have to amend the laws.
Under New Jersey law, Luers said, government agencies are required to post notice of a meeting in advance, and notify at least two newspapers of the meeting.
Additionally, Luers said, the meeting must start as an open meeting for the public to attend before board members go into a closed session, citing reasons such as personnel or legal matters that can be discussed in private.
Any meeting not publicly posted that starts off behind closed doors is "certainly not consistent with the spirit of the law," Luers said.
"As a matter of good government, good form and the law, it should have been posted," said Terry Mutchler, executive director of the Pennsylvania Office of Open Records.
If the DRPA were subject to Pennsylvania law, the agency should have given public notice of the meeting at least 24 hours in advance, Mutchler said.
"We've had questions about uniqueness of this authority and we've had it from both sides of the river," said Mutchler. "The authority has incredible power (including eminent domain and tax exemption) that affects the public."
Inquirer staff writer Amy Worden contributed to this article.