(NewsNation) —Renowned theoretical physicist Michio Kaku praised the work of Luis Elizondo, a former Pentagon insider who alleged the Department of Defense has a UFO retrieval program.

Kaku told NewsNation’s Brian Entin on Friday that Elizondo has “done a public service” by releasing a “mountain of classified data, which gives us hard numbers for the first time.”

Elizondo told NewsNation that the Department of Defense has a spacecraft crash retrieval program and has recovered nonhuman specimens. In a NewsNation special, Elizondo revealed more than any Pentagon official has done before, naming the government agencies and aerospace companies he says possess these alleged spacecraft.

Elizondo told NewsNation’s Ross Coulthart that the U.S. government recovered one of two unidentified anomalous phenomena, or UAP, during the infamous Roswell incident in 1947.

Kaku addressed his perceived limitations of what Elizondo exposed, as well.

“We have yet to see alien DNA,” Kaku said during an appearance on “Banfield.” “That would clinch it right off the bat. … That would clinch the whole debate: alien technology, alien transistors. We don’t have that. People talk about that, but we have yet to see evidence of alien technology that we scientists can then dissect in the laboratory. That’s a weakness of his story.”

The Department of Defense has rebuked Elizondo’s comments in a statement to NewsNation, denying the existence of any “credible evidence of extraterrestrial activity.”

“As we have stated previously, Luis Elizondo had no assigned responsibilities for the Advanced Aerospace Threat Identification Program (AATIP) while assigned to the Office of the Under Secretary of Defense for Intelligence and Security,” Sue Gough, a Department of Defense spokesperson, told NewsNation.

NewsNation’s Patrick Djordjevic contributed to this report.