Washington — Department of Homeland Security Secretary Alejandro Mayorkas said Sunday that the federal government was not notified about previous arrests by the suspect in the murder of Laken Riley, a 22-year-old nursing student. 

"Different cities have different levels of cooperation," Mayorkas said on "Face the Nation" on Sunday. "We were not notified in this instance."

• Transcript: Homeland Security Secretary Alejandro Mayorkas on "Face the Nation," March 3, 2024

Jose Ibarra, suspect in the murder of Riley, a Georgia nursing student, is an undocumented Venezuelan migrant who had been detained by U.S. Customs and Border Protection upon crossing into the country with permission to stay in the country on a temporary basis. The individual then went on to allegedly commit two offenses in New York and Georgia, according to Immigrations and Customs Enforcement. 

Mayorkas said that the federal government works closely with state and local law enforcement "to ensure that individuals who pose a threat to public safety are indeed our highest priority for detention and removal." But he made clear that different locales have "varying degrees of cooperation with immigration authorities."

"We firmly believe that if a city is aware of an individual who poses a threat to public safety, then we would request that they provide us with that information so that we can ensure that that individual is detained if the facts are warrant," Mayorkas said.

The comments come as immigration has begun to dominate the political discourse, with Republicans railing against the Biden administration for its handling of the southern border. Republicans have cited Riley's death and the suspect's migrant status as an example of the White House's failings on the border, as both parties have emphasized their support for enhanced border security. Days ago, President Biden and former President Donald Trump made dueling visits to Texas border towns, as the issue becomes a central one in the 2024 election.

As the two presumptive party nominees look toward the general election, Trump attempted to tie the suspect to Mr. Biden, describing Ibarra as a "monster illegal alien migrant released into the country" by Mr. Biden.

According to a CBS News/YouGov poll released on Sunday, Trump leads President Biden by four points nationally — 52% to 48% — in his largest lead to date.

Trump likewise has a significant advantage among voters when asked about the border, with 50% of voters saying Biden's policies increase the number of migrants trying to cross the southern border, while just 9% say the same of Trump's policies.