In December, O'Dowd said, he complied with a directive from Christie to ask the governor's then-deputy chief of staff, Bridget Anne Kelly, about her role.
Kelly - whom Christie would fire weeks later, after the disclosure of an August e-mail she wrote that read, "Time for some traffic problems in Fort Lee" - insisted she had nothing to do with the controversy, O'Dowd said.
He said he did not press other staff members at that time because Christie didn't direct him to do so.
O'Dowd is the highest-ranking Christie official to testify before the panel. He did not provide new information about the central questions the panel is trying to answer: who wanted the lanes closed, and why.
Assemblyman John S. Wisniewski, the panel's cochair, said O'Dowd's testimony revealed an apparent "lack of will" to determine "why this issue had percolated, at least from their perspective, into the governor's office."
Christie has maintained that he played no role in the controversy, which exploded in January with the disclosure of Kelly's "traffic problems" e-mail.
Lawyers hired by Christie pinned blame for the closures on Kelly and former Port Authority official David Wildstein, and said the plot seemed to be targeting the Democratic mayor of Fort Lee, who did not endorse the Republican governor's reelection. Wildstein resigned in December.
The lawyers, from the Gibson Dunn firm in New York, billed the state more than $3 million through February, according to an invoice released Monday by the state attorney general's office.
The office also disclosed the state would cover legal fees for 23 staff members in connection with the legislative probe, as well as an investigation by federal prosecutors into the lane closures.
Christie's nomination of O'Dowd - who worked for Christie at the U.S. Attorney's Office - as attorney general has not moved forward following the bridge controversy.
In Camden on Monday, Christie said he continued to support O'Dowd's nomination and expected that "after today, that'll be a conversation Kevin and I will have."
Christie said "it wasn't just [O'Dowd's] obligation" to respond to the bridge controversy, noting the involvement of McKenna.
While O'Dowd's testimony mostly matched what he told Christie's lawyers, according to a summary of the interview released by the firm, he contradicted some of the firm's report. The firm said McKenna reported not having a conversation about the lane closures until November, but O'Dowd recalled a conversation with McKenna and Christie that touched on the issue in October.
O'Dowd also contradicted testimony from other aides and the Gibson Dunn report portraying Kelly as erratic and insecure.
O'Dowd said he had a "very high opinion" of Kelly, whom he described as "hardworking, energetic and loyal." He believed her when he asked during a phone conversation on Dec. 12 whether she had "anything to do with closing the lanes," and she replied, "Absolutely not."
Much of Monday's testimony centered on the period around Dec. 12, when O'Dowd said Christie directed him during a meeting at the governor's mansion at Drumthwacket to question Kelly about her role in the closures.
O'Dowd said Christie told him that "all the noise about politics and political retribution" had become "a major distraction."
Christie's former campaign manager, Bill Stepien, was also at Drumthwacket that day. Christie told O'Dowd he had spoken to Stepien and did not believe he was involved, O'Dowd said.
Christie has since cut ties with Stepien, who exchanged e-mails with Wildstein disclosed in January that were derogatory toward Sokolich.
Stepien, who like Kelly has refused to provide documents to the panel, attended part of the hearing with lawyer Kevin Marino. The state disclosed Monday that it would pay Marino $175,000 for representing Stepien, who worked in Christie's administration before April 2013.
In addition to talking to Kelly on Dec. 12, O'Dowd said he met that night with Bill Baroni, a Christie appointee at the Port Authority, to tell him his resignation would be effective the next day. Baroni has testified to the Legislature that the lane closures were part of a traffic study.
Christie held a news conference the next day to announce Baroni's resignation. Before the conference, O'Dowd said, Kelly gave him an e-mail she had received while the lane closures were underway, from another staffer describing an "extremely upset" Sokolich.
"It surprised me that I had not heard about this sooner," O'Dowd said, adding that he shared the e-mail with Christie before the news conference.
During that conference, Christie said his staff had assured him they didn't have "any knowledge about this."
O'Dowd said Christie's remark seemed "inconsistent" with his knowledge of the e-mail to Kelly, but that the question at the time was whether the governor's staff had been involved in the closures, and the discrepancy did not strike him as significant.
Wisniewski later called O'Dowd's testimony "a significant development in this investigation."
Inquirer staff writer Julia Terruso contributed to this article.