Senator Chris Van Hollen said on Friday that Kilmar Armando Abrego Garcia, the Maryland man mistakenly deported by the Trump administration, reported having been traumatized inside a maximum-security prison in El Salvador before being transferred to another detention facility, where he remains in isolation.

The Maryland Democrat, who traveled to El Salvador to press for Mr. Abrego Garcia’s release and ended up meeting with him in San Salvador, said that Mr. Abrego Garcia had been transferred nine days ago from the Terrorism Confinement Center, or CECOT, to a lower-level facility in Santa Ana.

“He said that the conditions were better at this new detention center, but he was still in a total blackout,” Mr. Van Hollen said in an interview before arriving back in Washington. “No news from the outside world. Can’t speak to anybody at all.”

At a news conference at Dulles International Airport after returning, Mr. Van Hollen said that Mr. Abrego Garcia had told him that during his nearly three weeks at the maximum-security prison, “he was not afraid of the other prisoners in his immediate cell, but that he was traumatized by being at CECOT and fearful of many of the prisoners in other cell blocks who called out to him and taunted him in various ways.”

During their meeting Thursday evening, Mr. Abrego Garcia shared details with Mr. Van Hollen about his initial arrest and his time at CECOT, which El Salvador’s government says holds some of the most dangerous criminal gang members.

Mr. Abrego Garcia described having been detained and taken to Baltimore, where he had asked to make a phone call but had been denied. He was then taken to a detention facility in Texas before being handcuffed and shackled, put on a plane with blacked-out windows with other deportees and eventually deposited at CECOT.

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