But there is not link to terrorists according to the FBI. Of course they also admit that they have no idea who left it so it could be terrorists:

Police in Las Vegas, Nevada, are investigating the discovery of what they said is the deadly poison ricin in a hotel room.
Preliminary tests show the substance is ricin, authorities said, but other tests to confirm it are under way.
Meanwhile, the reason the substance was in the room remains a mystery.

“We don’t know who [the ricin] belongs to or why it would be here at this time,” said Capt. Joe Lombardo of the Las Vegas Metropolitan Police Department.
The FBI, which is assisting in the case, said it saw no link to terrorism, according to spokesman Richard Kolko.
Authorities were called to an Extended Stay America hotel around 3 p.m. PT Thursday after a man brought a bag with a small container to the manager’s office. The man said he found it while retrieving items from a hotel room.
[…]
Gupta said there are three ways of exposure to ricin: inhalation, ingestion or injections. If inhaled, people may develop fever, a cough, nausea, fluid in the lungs and organ failure.
There is no specific test for exposure and no antidote once exposed, he said.