Congress must investigate the “inhumane” and “un-American” use of solitary confinement in United States immigration detention centers, U.S. Senator Richard Bluementhal said in a statement released Friday.

Blumenthal, a Democrat from Connecticut, was responding to Solitary Voices an investigation by the International Consortium of Investigative Journalists and media partners in the U.S., Mexico, Guatemala, and the Dominican Republic that chronicled widespread misuse and overuse of isolation in facilities under the control of U.S. Immigration and Customs Enforcement, or ICE.

ICE used solitary confinement to isolate thousands of the most vulnerable immigrant detainees, including people with severe mental illness, LGBTQ people and the disabled, for weeks and months at a time, the reporting team found.

“This report should shock the conscience of every member of Congress,” Blumenthal said in the statement, which was sent to NBC News, an ICIJ partner. “Putting immigrants fleeing for their lives in solitary confinement, alone and away from any human contact for days, weeks, months is inhumane. It is un-American.”

ICIJ’s reporting was grounded in an analysis of more than 8,400 incident reports covering nearly five years that describe solitary confinement places.

Ellen Gallagher, a supervisor at the U.S. Department of Homeland Security, told ICIJ that she had reviewed internal reports for years that described abusive practices, and had tried and failed to get her agency to make meaningful reforms.

“People were being brutalized,” said Gallagher, speaking publicly for the first time. ICE’s use of solitary confinement “rises to the point of torture,” she said.

In his statement, Blumenthal called on Congress to summon Gallagher to testify.

“We must open an investigation, seek testimony from DHS whistleblowers and hold individuals responsible for these abhorrent conditions and policies,” his statement said. “Our country can—and must—do better to live up to our values.”

Earlier this week, Ilhan Omar, a Democratic Congresswoman from Minnesota, a frequent ICE critic, said in a tweet that “solitary confinement is torture” and that “we must ban ICE.”

Solitary confinement is torture. It’s time we abolish ICE. https://t.co/lqeYIXbKi5 — Ilhan Omar (@IlhanMN) May 21, 2019

ICIJ’s investigation was conducted over five months in collaboration with Grupo SIN in the Dominican Republic; Plaza Pública in Guatemala; Mexicanos Contra la Corrupción in Mexico; and The Intercept, NBC News and Univision in the U.S.