He killed three people in Spain and fled to Venezuela, where he was sentenced to 30 years in prison, court documents show. Then last week, the Trump administration negotiated his release as part of a large prisoner swap, and he arrived on American soil.

Now, the convict, Dahud Hanid Ortiz, 54, a U.S. Army veteran, is free in the United States, according to two people with knowledge of the case. One said he was in Orlando, Fla.

When the Americans put Mr. Hanid Ortiz on a plane on Friday back to the United States, at least some people in the Trump administration knew of his criminal past, according to a third person.

Mr. Hanid Ortiz was among 10 Americans and U.S. legal permanent residents extracted by the United States from detention in Venezuela on Friday. In exchange, the United States agreed to allow the release of 252 Venezuelan men it had sent to a maximum-security prison in El Salvador.

The Trump administration claimed all the men were members of the Tren de Aragua gang and had to be removed to protect the security of Americans.

President Trump had used a wartime power, the Alien Enemies Act, to expel them. His administration provided little evidence to back its claim that they were all criminals.