Harvard researcher Kseniia Petrova, already facing possible deportation back to Russia, has now been charged with smuggling undeclared biological material into the U.S.

Kseniia Petrova, the Harvard researcher who was detained by customs agents in February, faces a maximum sentence of up to 20 years in prison, a judge said Thursday.

Federal prosecutors allege Kseniia Petrova violated customs law by failing to declare preserved frog embryos in her luggage, in a case that's raised questions over her detention.