Katherine M. Sinderson

Threshold rulings and active discovery

Sinderson’s matters require different forms of proof: merger disclosures, pharmaceutical science, consumer-company accounting, mortgage lending, bank loan-loss reserves, aviation safety, beneficial-ownership filings, and medical-device regulation. Her teams connect internal documents and testimony with regulatory, scientific, accounting, market, expert, damages, and class evidence as each case advances.

Sinderson co-leads the Boeing and Twitter securities actions. In Boeing, a Mississippi public pension system serves as lead plaintiff in claims concerning statements about the safety and financial prospects of the 737 MAX program after the 2018 and 2019 crashes. The court denied the defendants’ dismissal motion in substantial part in 2022 and again sustained substantial portions of the amended claims in September 2024.

The Boeing team organized technical safety information, executive statements, market disclosures, and investor-loss allegations through repeated pleading challenges. With the claims sustained, discovery could test those public statements against internal documents, witness testimony, and expert evidence.

Musk crossed five percent of Twitter on March 14, 2022, and did not say so until April 4. Sinderson’s clients are the people who sold while the market did not know. In March 2025, the court denied the dismissal motion in substantial part, preserving the sellers’ claims and allowing discovery into transaction records, communications, disclosure duties, intent, and price effects.

That action turns on the timing and content of beneficial-ownership disclosures, the trades made before the public filing, and the market response once the position became known. Sinderson’s team moved those questions from the pleading record into evidentiary development.

With John Rizio-Hamilton, Sinderson also leads the iRhythm securities action concerning statements about the Zio AT heart-monitoring device. After the court sustained core claims, it rejected the defendants’ 2025 request for judgment on the pleadings, allowing continued development of the regulatory, technical, marketing, and market evidence.

The iRhythm record concerns the device’s capabilities and intended patient population, along with regulatory communications, product marketing, revenue forecasts, technical operation, and later market disclosures. The 2025 ruling preserved the action through a second merits challenge and allowed that combined record to continue developing.

Near-trial investor recoveries

In the Bank of America securities litigation, public pension funds challenged statements made before the shareholder vote on the company’s acquisition of Merrill Lynch, including disclosures concerning Merrill’s losses and compensation. Sinderson served as an integral member of the trial team.

The parties reached a $2.425 billion agreement when the case was close to trial. The court approved the settlement in 2013, creating a cash fund and corporate-governance measures after the team had developed witnesses, documents, expert positions, and presentations of liability and damages.

In Merck, investors challenged statements and omissions concerning the pain medicine Vioxx. Sinderson served as a leader on the trial team in litigation that combined scientific evidence, drug marketing, regulatory history, market disclosures, and loss analysis and ultimately produced a $1.062 billion settlement.

Both matters were developed through pleading, discovery, expert work, and motion practice before the approaching trial dates. The teams had prepared specialized evidence, witnesses, and jury presentations addressing materiality, causation, and damages when the resolutions were reached.

Discovery and resolution

Sinderson led the Kraft Heinz team for public pension fund clients in claims involving the company’s financial position, asset values, margins, and cost-cutting strategies. The litigation resolved for $450 million in cash, and the court-approved distribution process began in 2025.

The Kraft record joined internal and operational evidence with accounting analysis, expert work, market disclosures, and investor-loss evidence. That development tested the company’s reported asset values and operational savings before the proposed recovery entered the approval and distribution process.

Sinderson and Hannah Ross led the Washington Mutual action for investors in common stock, debt, preferred securities, and offerings. Resolutions with officers and directors, underwriters, the auditor, and other parties produced more than $215 million in total recoveries.

The Washington Mutual work required reconstruction of the bank’s home-lending operations across multiple securities and defendant groups. The team coordinated differing statements, legal provisions, defenses, insurance positions, and payment sources while maintaining a common evidentiary account of the bank’s condition.

In Wilmington Trust, public pension fund clients alleged that the bank concealed deterioration in its loan portfolio and understated loan-loss provisions. Sinderson served as lead partner through amended pleading, parallel investigations, criminal proceedings, discovery, a bank-examination privilege dispute, and a related stay. The civil litigation ultimately produced a $210 million recovery.

Information emerging from the parallel proceedings informed the amended pleading, while the privilege dispute and stay shaped the timing and scope of discovery. Sinderson kept the civil claims moving through those overlapping developments to a court-supervised resolution.

Appeals and additional recoveries

In the Six Flags securities litigation, Sinderson led the team through repeated dismissal motions and two favorable Fifth Circuit rulings before securing a $40 million settlement. The appellate decisions preserved the investors’ claims and allowed the case to proceed toward a funded resolution.

In Grand Canyon Education, Sinderson’s team defeated a dismissal motion and advanced the case into discovery before securing a $25.5 million settlement in 2024. The ruling allowed the investor team to obtain and test evidence before negotiating the court-supervised recovery.

In both matters, the litigation continued beyond threshold challenges into the evidentiary record needed for settlement review. The resulting funds then proceeded through notice, allocation, judicial approval, claims administration, and distribution for eligible investors.

Institutional investor representation and professional leadership

Sinderson represents public pension funds and other investors through pleading, document production, class responsibilities, discovery, expert development, trial preparation, mediation, approval, allocation, and distribution.

Those clients review pleadings, preserve and produce records, participate in discovery when required, consider class responsibilities, and authorize settlements. Sinderson works with their fiduciaries as the record develops so they can evaluate amendments, appeals, continued discovery, mediation, trial preparation, and proposed relief.

In 2025, she participated in a Practising Law Institute program, “Securities Litigation 2025: From Investigation to Trial,” on a panel devoted to mediation and settlement. She also co-chairs the Federal Bar Council’s Securities Litigation Committee and lectures on expert-witness and litigation-risk issues.

The Bank of America case settled close to trial — witnesses prepared, experts ready, the presentation a jury would have seen already built. Merck settled the same way. Neither jury was ever seated.