Colorado Democrats in Congress are continuing to call for an independent investigation into Ace of Spades “death cards” that were found on the cars of people detained by Immigrations and Customs Enforcement in Eagle County.

U.S. Rep. Joe Neguse, whose district includes Eagle County, and Sens. John Hickenlooper and Michael Bennet sent a letter to U.S. Department of Homeland Security Secretary Kristi Noem on Tuesday. The letter calls on Noem, who President Donald Trump fired last week but is expected to remain in the job through the end of the month, to disclose which ICE field office is investigating the incident.

“We remain deeply concerned by the allegations that federal agents were falsely acting as local law enforcement and that the ace of spades, long known as the ‘death card,’ was used to intimidate Latino communities,” the lawmakers wrote.

In January, ICE agents in unmarked vehicles with sirens conducted “imitation traffic stops” that resulted in several Latino individuals being detained in Eagle County, according to the lawmakers’ letter. 

The immigration advocacy group Voces Unidas reported that when family members of those detained went to pick up the abandoned vehicles, they discovered the Ace of Spades cards inside. The cards were printed with the ICE Denver Field Office address and phone number.

The Ace of Spades, known as the “death card,” has a long history as a tool of intimidation and has been used by white supremacists groups to demean people of color, according to Voces Unidas.

ICE Denver public affairs stated in January that it “unequivocally condemns this kind of action” and the Department of Homeland Security is conducting an internal investigation into the cards. The agency has not responded to multiple requests for information on the people detained in Eagle County and what charges they are facing.

Additional Ace of Spades cards have also been found in other Colorado counties, according to the lawmakers’ letter. 

In February, the Democratic lawmakers asked Noem to provide briefing on ICE activities in Eagle County, a written report on the investigation into the incident and written confirmation of any disciplinary or corrective actions taken. The lawmakers also asked for an independent investigation by the Department of Homeland Security’s Office of the Inspector General.

Noem responded to the February letter, but did not provide the items requested, according to Neguse’s Office. Instead, she told the lawmakers that the Office of the Inspector General referred the case to the Office of Professional Responsibility, which assigned the incident to a field office for investigation.

“As a law enforcement agency, ICE holds all its employees to the highest standards of integrity and professional conduct,” Noem wrote in response to the lawmakers. “ICE takes allegations regarding professional misconduct seriously and the ICE Office of Professional Responsibility investigates allegations of misconduct appropriately.”

She added that ICE does not comment on ongoing investigations and is currently “not at liberty” to provide additional information.

Neguse’s Office said in a news release that the Department of Homeland Security’s failure to disclose which field office is investigating the Ace of Spades cards, “raises serious concerns about transparency and possible conflicts of interest.”

The Democratic lawmakers gave Noem until March 20 to respond to their latest letter.