(CNN) -- Police in Las Vegas, Nevada, are investigating the discovery of what they believe to be ricin at an extended stay hotel Thursday. Authorities were called to an Extended Stay America hotel after staff found a suspicious substance in one of the rooms. "They determined it might be some biological agent, and through presumptive tests, we determined it to be ricin," said Capt. Joe Lombardo of the Las Vegas Metropolitan Police Department. "We don't know who it belongs to or why it would be here at this time." Three hotel employees and a fourth person who came to the...