The FBI has taken over the investigation into how the poisonous material ricin found its way into a student's apartment in Dinkytown, Minneapolis.
In an updated statement on Wednesday, the FBI Minneapolis says a preliminary test of the substance found at the building on the 500 block of 14th Avenue SE "indicated the presumptive potential presence of ricin."
A female University of Minnesota student took herself to a hospital after coming into contact with the potentially lethal material.
Hundreds of people, many of them students, were evacuated from the apartment building after the report came in, with WCCO reporting that students were told to leave everything behind – even their pets – as they exited the building.
The FBI is investigating the substance because ricin is classified as a biological weapon of mass destruction (WMD).
The FBI's Hazardous Evidence Recovery Team (HERT) was at the apartment on Wednesday, receiving assistance from the Minnesota National Guard.
"The purpose of the FBI activity in the apartment in question ... is to recover any and all evidence of any potentially dangerous material," the FBI statement said.
"Once collected and secured, the evidence will be delivered to the FBI lab in Quantico, Virginia for testing and positive identification."
Ricin can quickly become lethal to humans when inhaled or injected, and extremely dangerous (though slower acting) when ingested. It is a poison that occurs naturally in castor beans, and the CDC calls accidental exposure to the substance "highly unlikely, except through the ingestion of castor beans."