The choice was unconventional: Eric Adams, the candidate who would go on to win the 2021 election for mayor of the nation’s financial capital, had picked an inexperienced 23-year-old to run his campaign’s fund-raising operation.

Ostensibly, the fund-raiser, Brianna Suggs, did her job. Thanks in part to her work, the campaign would spend more than $18 million and win the election.

But the unusual arrangement, which raised eyebrows in the tight-knit, professional world of Democratic political fund-raising, might have come at an extraordinary cost.

On Thursday morning, federal agents raided Ms. Suggs’s home in Brooklyn and walked away with a wide range of materials, including three iPhones, two laptop computers and a manila folder labeled “Eric Adams.” The court-authorized search was part of an expansive public corruption investigation into whether the campaign conspired with the government of Turkey to receive illegal foreign donations.