She sought to prove her grandfather was poisoned at Camp Lejeune. Records she found could help thousands.

Leo Case survived the battle of Iwo Jima and risked his life to save his crew during a clash in the South Pacific — only to die of multiple cancers at 58.

The World War II tank commander and recipient of the Navy Cross, the military’s second-highest recognition for valor, was one of the first service members exposed to a contaminated water supply at Camp Lejeune.

His granddaughter sought to prove he was sickened at the Marine Corps training facility in North Carolina. In the process, she amassed an archive of records that she said could help thousands of other veterans and their loved ones bolster their challenging water contamination cases.

“It’s become very personal,” said Jessie Hoerman, 55.

Hoerman, an attorney in St. Louis, has spent the last two years scouring eBay, antique stores and national archives to find muster rolls, phone directories, yearbooks and other materials that could substantiate her family’s claim.

Now, she plans to share what she believes is the largest private collection of Camp Lejeune materials with the veterans named in her documents.

“I want to go and find these families,” she said. “I want to give these hard copies back.”

In one of the largest water contamination cases in U.S. history, up to 1 million people who lived or worked at Camp Lejeune from August 1953 to December 1987 may have been exposed to a drinking water supply contaminated with chemicals that have been linked to severe health problems, federal health officials said.

Multiple sources contaminated the wells, including waste from a nearby dry-cleaning facility and leaks from underground storage tanks on base, according to the Agency for Toxic Substances and Disease Registry.

There were extremely high levels of trichloroethylene, tetrachloroethylene, vinyl chloride and benzene — colorless chemicals that can cause several diseases, including cardiac defects and some cancers, the ATSDR said.

Case died of bowel, colon, liver and lung cancer in 1976. The Veterans Administration hospital that treated him in Syracuse, New York, conducted a postmortem examination and found no evidence of any hereditary or infectious disease, according to a letter it sent the family that was provided to NBC News.

Hoerman said she started digging into her grandfather’s history after the PACT Act of 2022 expanded benefits to millions of veterans exposed to burn pits and other toxic substances.