The exclusive story's foundation was laid months ago, when questions arose about Melania Trump's immigration history and AP contacted employees at the modeling firm where she worked in the 1990s. No office records from the time were found at first. But AP's questions were asked, and one ex-worker kept searching through storage.

Finally, the documents turned up, and when the worker pointed AP to them, they became the basis of a story showing that the future wife of Donald Trump, who has taken strict stands on immigration enforcement, was paid for modeling jobs worth tens of thousands of dollars before she had permission to work in the U.S.

The AP's investigation, by Alicia Caldwell, Chad Day and Jake Pearson, earns the Beat of the Week.

The story, written and transmitted before Tuesday’s election, alluded to Trump's proposals to broaden use of the government's E-verify system to check whether job applicants are authorized to work, adding, "He has noted that federal law prohibits illegally paying immigrants."

They showed that she was paid for 10 modeling assignments between Sept. 10 and Oct. 15, 1996, during a time when her visa allowed her to be in the U.S. and look for work but not to perform paid work in the country.

It also quoted Mrs. Trump's statements that she never violated terms of her immigration status. "During the presidential campaign, she has cited her story to defend her husband's hard line on immigration," the story said.

In August, Pearson scoured old New York state court records from a 1990s-era civil lawsuit involving the business partners of the now-defunct modeling agency that facilitated the future first lady's early U.S. work. Day and AP's Jeff Horwitz contacted former employees, establishing a rapport with some. It was later, when Day and Caldwell teamed up on two stories scrutinizing Mrs. Trump's immigration timeline, that a source alerted reporter Jill Colvin and Day to documents that indicated she had worked without the proper visa.

Working with editor Ted Bridis, Caldwell, Day and Pearson conducted a rapid but thorough effort to authenticate the sensational documents, cross-referencing them against information obtained from earlier interviews with key figures and additional records from sources and court files.

They showed that she was paid for 10 modeling assignments between Sept. 10 and Oct. 15, 1996, during a time when her visa allowed her to be in the U.S. and look for work but not to perform paid work in the country. http://apne.ws/2flJIkY

The AP story, published Nov. 4, was the third-highest trending topic on Twitter worldwide through the weekend, and the most-read on AP News.com across the weekend. The Nerve Center's Mark Davies said readers spent an aggregate 472,000 minutes, or 7,866 hours, actively engaged in reading the story, according to Chartbeat metrics; in social media interaction, it had 348,000 likes, shares, comments and retweets, as measured by NewsWhip.

For ferreting out decades-old documents to support strong accountability reporting, Pearson, Day and Caldwell win this week's $500 prize.