On a lazy Sunday in March 2012, I was headed out to run errands when CNN's Anderson Cooper 360 turned to a broadcast called "Eugenics in America". The report recounted the sad history of minorities, prisoners, the poor and the disabled being forcibly sterilized during the early 20th century.

No news there, right? Yet, I was taken aback when the piece focused on California's role. I never knew the Golden State led the nation with nearly 20,000 sterilizations. Nor did I know that Nazi Germany consulted with California's eugenics leaders in the 1930s. I also was surprised that CNN's reporter was unable to get lawmakers in Sacramento to talk about this.

I set out to learn more. Were there any living victims? If so, how many and how could I find them?

Coincidentally, soon afterward, I received a tip that sterilizations may have occurred in California's women's prisons as recently as 2010. The assertion shocked me. It sounded outlandish.

By then, I knew that California lawmakers had banned forced sterilizations in 1979. Since 1994, elective sterilizations have required approval from top medical officials in Sacramento on a case-by-case basis. Had that happened in these cases?

I sought out the prisoner rights organization Justice Now and traveled to its Oakland office. Advocates showed me state spreadsheets indicating contract doctors were reimbursed for performing tubal ligations on inmates. The group's data was incomplete. It lacked the amounts paid. And there was no information on who was sterilized or whether the procedures were approved at headquarters. But at a minimum, the documents showed that the tip wasn't as off base as it first appeared.

The missing information foreshadowed the difficulties that would come in the months ahead as I sought to fill in the blanks. Intense secrecy governs these surgeries. Strict state and federal laws protect patient privacy. Prison attorneys fought to deny access to key documents and records, including those not medically related. Also, inmates who have been sterilized are reluctant to talk about it for many reasons – some of which stem from shame and trauma from the surgery.

Still, I crisscrossed the state seeking and meeting people who could help break the silence. Over time, I obtained a more complete spreadsheet of tubal ligation procedures and costs. Prison officials talked to me both on the record and off. So did former and current inmates. A few medical records trickled in as well.

Highlights from the first story that The Center for Investigative Reporting published 7 July (which I authored) show the results, including:

• Doctors under contract with the California Department of Corrections and Rehabilitation sterilized nearly 150 female inmates from 2006 to 2010 without required state approvals – and there were perhaps 100 more dating back to the late 1990s.

• Former inmates and prisoner advocates say prison medical staff coerced the women into agreeing to the surgeries, targeting those deemed likely to return to prison in the future.

• From 1997 to 2010, the state paid doctors $147,460 to perform tubal ligations, according to a database of contracted medical services for state prisoners.

• A prison administrator acknowledged that she tried to find workarounds, and the prison's ob-gyn defended the expenditure, saying:

Over a 10-year period, that isn't a huge amount of money compared to what you save in welfare paying for these unwanted children – as they procreated more.

• One former inmate, who gave birth to a son in October 2006, said she repeatedly was pressured to agree to a tubal ligation, including while at the hospital under sedation for her C-section. "He said, 'So we're going to be doing this tubal ligation, right?' " she said. "I'm like, 'Tubal ligation? What are you talking about? I don't want any procedure. I just want to have my baby.' I went into a straight panic."

The story went viral on social media. News organizations and bloggers nationally and internationally circulated the piece, prompting intense debate. Lawmakers immediately denounced the sterilizations, which appear to have ended in 2010, and demanded answers. So far, two hearings have been held. A state audit was ordered and fast-tracked to determine what happened and who knew what when. And, of course, our investigative journalism work continues.