U.S. authorities announced on Monday the arrest of a Chinese researcher on charges of smuggling biological materials into the U.S., marking the second incident in recent days.

The FBI filed a criminal complaint against Chengxuan Han, identified as a Chinese doctoral student from the College of Life Science and Technology at Huazhong University of Science and Technology in Wuhan. Han was arrested on Sunday at the Detroit airport.

The complaint reveals that since September, Han has discreetly sent four shipments from China with biological material hidden, intended for a laboratory at the University of Michigan, where she aimed to work on a project for a year. Officials stated that Han gave false information about these shipments to federal agents when questioned upon her arrival from Shanghai.

Two Chinese nationals were charged last week after the FBI said it had been determined that one tried to smuggle a toxic fungus into the United States, also for research at the University of Michigan, it alleged. One, a researcher at the university, was arrested and remains in custody, while the other was denied entry to the United States last year and remains at large.

According to the complaint, the biological material Han is accused of smuggling — sometimes hidden between pages of a book — is related to roundworms and requires a government permit.

The complaint also alleges that Han deleted the contents of her electronic device three days before she arrived in Detroit.

“Han stated she deleted the content to ‘start fresh’ while she was in the United States,” it says.

Han is in custody ahead of a bond hearing Wednesday.

The Chinese Embassy in Washington did not immediately respond to an emailed request for comment outside business hours.

With regard to the two Chinese nationals who were previously charged, a spokesperson for the Chinese Foreign Affairs Ministry said last week that he was not aware of the situation but that the Chinese government “has always required Chinese citizens overseas to strictly abide by local laws and regulations, while also safeguarding their legitimate rights and interests in accordance with the law.”

The University of Michigan also did not immediately reply to a request for comment Monday outside business hours.

In a statement in response to the case last week, the university said it was cooperating with federal law enforcement and that it strongly condemned “any actions that seek to cause harm, threaten national security or undermine the university’s critical public mission.”

Victor Galea, a professor of plant pathology at the University of Queensland in Australia, said that while the fungus, known as Fusarium graminearum, is found in every part of the world where wheat is grown, a genetic variant from a different country “can be more aggressive or virulent, and so this is why we have biosecurity regulations to prevent people from moving fungal pathogens from one part of the world to the other.”

Similarly, while research material such as what Han is accused of smuggling can be moved between countries, it should be done “through all the appropriate agreements and controls,” Galea said.

The roundworms “could be damaging to crops or the environment, or it may be that they’re benign and they don’t do anything,” he said. “But you can’t determine that unless this is thoroughly investigated.”