The upheaval at the National Rifle Association claimed its latest casualty Thursday with the announced resignation of David Lehman, general counsel of the NRA Institute for Legislative Action in Washington, D.C., the group's powerful lobbying arm.

Lehman, who was with the nonprofit organization for 17 years, is the latest in a string of lawyers, executives and board members to leave the troubled NRA in the past four months. He could not be reached for comment Friday.

Lehman briefly filled the role of executive director and top lobbyist after the suspension, and subsequent resignation, of then-executive director Christopher Cox in June. Cox and Lehman were believed to have been supporters of ousted NRA President Oliver North.

In July, the pro-gun lobbying group named Jason Ouimet as interim executive director. He had previously been its director of federal affairs.

The Fairfax, Virginia-based NRA on Thursday also dismissed its longtime outside counsel, Charles Cooper, chairman of the D.C. law firm Cooper & Kirk.

The New York Times Friday published emails the newspaper obtained between Lehman and outside counsel Cooper that implied their link to North.

Another outside counsel for the NRA, Michael Volkov, a former federal prosecutor and head of the Volkov Law Group in D.C., also resigned on Thursday. In addition, the association reportedly has lost five board members since Aug. 1.

The NRA's turmoil began in April when a highly publicized power struggle arose between chief executive Wayne LaPierre and then-president North. North has accused LaPierre of financial improprieties.

The board backed LaPierre and ousted North on April 29, along with the board's own outside counsel, J. Steven Hart, who reportedly wanted the board to pursue North's allegations against LaPierre.

Amid the chaos in April, New York Attorney General Letitia James opened an investigation into the NRA'S tax-exempt status, which will allow her office to review the group's financial records. The NRA also broke in April with its Oklahoma-based advertising firm Ackerman McQueen, after a 38-year relationship. That led to a bitter lawsuit that is pending between the two.

North's ouster and subsequent financial demands resulted in the NRA suing North, and in North filing a counterclaim in July in the Supreme Court of New York. North is represented by Williams & Connolly.

The NRA has retained attorney William Brewer III, of Brewer, Attorneys and Counselors, with offices in Dallas and New York, as its outside counsel. North's suit alleged that LaPierre has "improperly" authorized payments of about $2 million a month to the Brewer law firm.

NRA general counsel and secretary John Frazer gave Corporate Counsel a statement Friday dealing with the relationship between the NRA and Brewer. "The firm represents the NRA on several matters—working to protect our legal, regulatory and reputational interests," Frazer's statement said. "As we've repeatedly stated, centralizing these services allows the NRA to gain strategic advantages, recognize cost savings, and, most importantly, improve our advocacy in the best interests of our members."

He added that besides his staff of 10 attorneys "with decades of cumulative in-house experience, we have a deep reservoir of capable outside attorneys, and continue to notch wins in important matters all over the country. As recent examples, we are making great strides in our legal action against New York Governor Andrew Cuomo and against the City of Los Angeles' anti-NRA blacklisting scheme."

In another statement Friday, Brewer said, "It's our privilege to assist the NRA on a variety of legal fronts. We initially came to represent the association in response to a corporate campaign being waged against it by a number of NGO's. Later, when Governor Cuomo and Maria Vullo, then superintendent of the New York State Department of Financial Services, announced a highly publicized 'blacklisting campaign' against the NRA, we were retained to press the association's First Amendment claims against those government officials."

He said the firm's work also includes representing the NRA in regulatory inquiries in New York and responding to a number of congressional inquiries.