Juan Sanchez, who built a business empire that has boomed on the back of a hardline government policy, will retire

A non-profit that detains thousands of migrant children on behalf of the Trump administration as the government continues its crackdown on immigration into the US, especially across the US-Mexico border, said on Monday its founder and chief executive is stepping down.

Southwest Key Programs announced on Monday that Juan Sanchez, who built a business empire that has boomed on the back of a hardline government policy, will retire. The company issued a short statement thanking him, without going into details about the exact circumstances leading up his decision to depart.

The Austin, Texas-based non-profit operates facilities at and near the US-Mexico border, collecting hundreds of millions of dollars annually through the US Department of Health and Human Services.

Southwest Key has come under fire as the Trump administration detained more immigrants and conducted large-scale separations of families in the last 18 months. Critics have accused Sanchez of facilitating the detention of thousands of children and questioned the salaries Southwest Key paid him and his family.

Federal prosecutors have been examining Southwest Key’s finances, according to reports in the New York Times, amid questions about whether the company misappropriated government funds.

The company has also been involved in allegations of sexual and physical abuse of minors in its custody, as well as the investigation into any financial impropriety.

On Monday Donald Trump issued a budget proposal from the White House demanding $8.6bn to construct his long-promised border wall, his latest demand for US public money, after he campaigned on a pledge that Mexico would be forced to pay for any such wall. Hardline policies have already curbed immigration to the US but there has been a surge in the number of families crossing from Mexico in recent weeks, which the government last week called a crisis.

Families have been forcibly divided when adults cross the border with children and are taken into custody by border patrol, then detained in separate facilities as they await legal processing. A fresh news report at the weekend said that separations have continued since the policy was officially ended in mid-2018.

The organization thanked Sanchez, saying “it’s time to begin a new chapter”.