Decades from now, when historians try to make sense of how the U.S. government treated detained migrants, they will be able to hear directly from the men and women in federal immigration detention centers.

At least that’s the hope of Lisa Lamont, head librarian at San Diego State University, who oversees a collection of more than 1,700 letters written by migrants in detention centers.

“In 20, 30, or 40 years, or even longer down the road, when researchers are researching this time in U.S. history, I think these letter are going to be invaluable,” she said.

The population of people in Immigration and Customs Enforcement custody has grown significantly under the Trump administration. During fiscal year 2015 there were 28,449 unauthorized immigrants in detention facilities. That number increased to 38,106 and 42,188 in the 2017 and 2018 fiscal years, respectively. Projections show that number is expected to increase to 52,000 by the 2020 fiscal year, according to data from the federal government.

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