Lawyers cannot find the parents of 545 migrant children whose parents were separated from them, under a 2018 Trump administration “zero tolerance” policy. About two-thirds of those parents had been deported to Central America without their children, the American Civil Liberties Union stated Tuesday in a filing.

The ACLU and other pro-bono law firms began working to find the separated family members in 2017, when the Trump administration began their pilot program of the policy.

More than 1,000 parents separated from their children during the pilot program had been deported before a federal judge in California ordered that they be found. When the 2018 policy was ended via executive order, most of the separated families were still in custody.

“People ask when we will find all of these families, and sadly, I can’t give an answer. I just don’t know,” said Lee Gelernt, deputy director of the ACLU Immigrants’ Rights Project. “But we will not stop looking until we have found every one of the families, no matter how long it takes. The tragic reality is that hundreds of parents were deported to Central America without their children, who remain here with foster families or distant relatives.”

Some of the families that have been successfully contacted chose to keep their children in the U.S. with family members or sponsors “due to fear of what will happen to their child if they return” to their home country.

White House spokesperson Brian Morgenstern appears to have used that as a talking point, when asked by NBC about the Department of Homeland Security report that prompted the law firms to begin reconnecting families.

Morgenstern claimed many of the parents “have declined to accept their children back… It’s not for lack of effort on the administration’s part.”

Gelernt shot back saying, “First, we have not even found these 545 parents so neither we nor certainly the administration can know whether they want to be reunited.”

“Second, in the past there have certainly have been parents who have made the agonizing decision to leave the child in the U.S. because of the danger the child would face upon return,” he continued. “The humane and simple solution is for the Trump administration to allow the parents to return to the U.S. to reunite with their children but the administration is not allowing that.“