The Republican National Committee’s Washington headquarters was briefly evacuated on Wednesday as police investigated two vials of blood that had been addressed to former President Donald Trump following the presumptive presidential nominee’s takeover of the national party apparatus.

Hazardous-materials teams were called in after the vials were discovered, according to the U.S. Capitol Police, who said they would continue to investigate. It was unclear if anyone came into contact with the blood and to whom it belonged.

The vials were addressed to Trump, according to a person familiar with the situation but not authorized to speak about it publicly. It was unclear whether any message accompanied the vials explaining why they were sent.

The RNC chairman, Michael Whatley, decried the “revolting attack” but did not offer more details.