A senior Department of Homeland Security official was unable to tell Congress the number of Syrian refugees who have entered the United States in the last year and the number of Americans who have travelled to Syria and returned, in testimony on Capitol Hill that angered many lawmakers.

Kelli Ann Burriesci, a deputy assistant secretary in the department’s office of policy, could not provide statistics about immigration when the House’s national security subcommittee grilled her about potential flaws in the visa waiver program.

While lawmakers had requested that its secretary, Jeh Johnson, testify before the committee, the agency sent Burriesci instead, saying that she is the resident expert on these issues.

However, Burriesci struggled to answer questions, prompting anger from lawmakers and concerns that the department is failing to track potentially dangerous immigrants.