Superior Court Judge Mary C. Jacobson's opinion, released Wednesday, "clarified and strengthened this legislative committee's authority to grant immunity," Wisniewski said in an interview.
Offering immunity, however, could interfere with a concurrent federal investigation into the lane closures by the U.S. Attorney's Office. Wisniewski said his panel would confer with outside counsel Reid Schar, a former assistant U.S. attorney, before taking that route.
Jacobson ruled that the subpoenas violated Kelly's and Stepien's Fifth Amendment right against self-incrimination.
But she said more specific subpoena requests might be permissible - an option Wisniewski said the panel would consider - and suggested a grant of immunity could be another means of obtaining the documents. The panel could also appeal the judge's decision.
In the interim, the panel is asking the law firm retained by Christie's office to provide summaries or other documents related to the 70 interviews the firm conducted as part of its own review of the lane closures.
The firm, Gibson Dunn & Crutcher, released a report last month absolving the Republican governor and his current staff of any responsibility for the traffic jams, which the firm said were orchestrated by Kelly and David Wildstein, a former Christie appointee at the Port Authority of New York and New Jersey.
Documents released by legislators show Kelly wrote an e-mail in August calling for "traffic problems in Fort Lee," to which Wildstein responded, "Got it."
If Gibson Dunn does not comply with the request by Friday, the panel will issue a subpoena demanding the information, Wisniewski said.
The committee has issued 28 subpoenas since it was formed in January, and most recipients have fully complied, he said.
Wisniewski said the committee is still poring over documents, and could move to compel oral testimony as soon as May.
Republicans - who make up a minority on the panel, as they do in the Legislature - say the judge's decision Wednesday points to the need for the committee to consider changes to the Port Authority, which operates the bridge.
"We're legislators. We're not prosecutors. And consequently, our goal is to do things to reform what goes on at bistate agencies that have been out of control," Assembly Minority Leader Jon Bramnick (R., Union) said. "We know enough now to move some legislation."
Specifically, he supports a package proposed by Assemblywoman Amy Handlin (R., Monmouth) that calls for an independent monitor with subpoena power to oversee the agency and would require greater financial disclosure for top agency officials, among other provisions.
Senate President Stephen Sweeney (D., Gloucester) also was hesitant this week about continuing the investigation, noting that federal prosecutors were involved and legal costs were growing. He later released a statement saying he was committed to the probe.
Wisniewski said the committee still didn't know the "full extent of the problem" and therefore couldn't propose meaningful solutions. "We're not going to get a second bite at the apple in doing this," he said. "So getting it right is going to be very important."