US prosecutors drop criminal charges against scientist detained over frog embryos

Federal prosecutors have dropped all criminal charges against a Russian scientist who spent four months in immigration detention after flying into Boston with frog embryos intended for cancer research at Harvard Medical School.

Kseniia Petrova, 31, was arrested in March 2025 after returning from a vacation in France, where she had visited a laboratory specializing in cutting extremely thin sections of frog embryos. During her visit, she obtained a package of samples for her research back in the US.

Customs officials questioned Petrova about the samples when she arrived at Logan international airport. She was later charged with smuggling, concealing facts and making false statements to government officials.

Petrova's case was one of the many shocking, high-profile, immigration-related arrests, especially involving academics, in the early months after Donald Trump returned to the White House promising a crackdown on immigration.

Petrova had fled Russia after being arrested for protesting against the invasion of Ukraine, and colleagues at Harvard University called her research talents "spectacular".

On Wednesday, the US district judge Leo Sorokin granted prosecutors' request to dismiss all charges against Petrova without holding a hearing.

The case began unraveling when a federal judge determined that a customs officer had improperly canceled Petrova's visa. Petrova had feared that she would be deported to Russia, where she could face imprisonment. In May of last year, a judge ordered her release.

Her attorneys had challenged the criminal prosecution, arguing that the charges were vindictive and had been filed only after it appeared Petrova would prevail in her immigration case. They maintained that criminal prosecutions involving conduct like hers were uncommon.

On Tuesday night, the US attorney Leah Foley submitted a motion seeking to dismiss the case "based on developments in this case and an assessment of the office's priorities and resources".

"At this stage, the resource costs of continuing this prosecution outweigh the public interest in its resolution," she wrote, adding that the "defendant's claims of vindictive and selective prosecution are meritless".

Following the dismissal, Petrova's attorney Daniel Marx criticized the decision to pursue criminal charges against the scientist.

"The DOJ never should have brought this highly unusual 'smuggling' prosecution against Kseniia Petrova, a talented scientist at Harvard," Marx said in a statement. "Ms Petrova only sought to advance medical research into aging that could benefit everyone, and her handling of scientific samples – inert, non-living, non-toxic, frog embryos – never posed any danger to anyone."

The Department of Homeland Security (DHS) had continued to defend Petrova's arrest, maintaining that she had lied to federal officers about the frog embryos.