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 during nearly three weeks inside a notorious 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 he had been transferred nine days ago from the CECOT prison 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 of Mr. Abrego Garcia in an interview before arriving back in Washington from the visit. “No news from the outside world. Can’t speak to anybody at all.”

At a news conference at the airport after returning, Mr. Van Hollen said that Mr. Abrego Garcia had said that during his time 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 time at CECOT, which houses some of the most dangerous criminals in the nation and is known for human rights abuses. He described having been detained and initially taken to Baltimore, where he had asked to make a phone call but been denied. He was then taken to a detention facility in Texas before being handcuffed and shackled, placed on a plane with blacked-out windows with other deportees, and eventually deposited at CECOT. There, he was placed in a cell with about 25 others, according to Mr. Van Hollen.

“He said that he felt very sad to be in a place that’s meant for criminals,” Mr. Van Hollen said of Mr. Abrego Garcia, a Salvadoran migrant who entered the United States illegally but was given a deportation reprieve in 2019. “That’s not who he is.”