The threats were apparently made after an altercation with two passengers on the bus, according to Schmaling.
"(He) has been in our country illegally and has been deported some time ago back to Mexico and by virtue of his actions last night, he's back and threatening to kill Americans", Racine County sheriff Christopher Schmaling said. The ordeal started near Milwaukee when police said they got a call from someone on board the Greyhound bus.
Police put out spike strips on I-94, which brought the Greyhound bus to a stop on an exit ramp to Route 173 in Lake County, Illinois.
Numerous police agencies from Wisconsin and IL are responding to an incident involving a Greyhound bus.
The "disorderly and possibly armed subject" was taken into custody, authorities said. Authorities say the man, 33-year-old Margarito Vargas-Rosas, is in the USA illegally and has been deported before.
Multiple police agencies were on the scene and motorists are advised to avoid the area.
Schmaling said Vargas-Rosas lives in Chicago but works at a restaurant in Milwaukee. "He did make threats that he was going to shoot and kill".
According to Schmaling, the driver of the bus didn't realize deputies were attempting to pull the vehicle over. "(The police) were in front of us, they were in back of us".
The suspect is now being held at the Lake County, Illinois, jail. The driver says he didn't pull over because he thought the incident was a training exercise, despite passenger's pleas for him to stop. "You need to stop" and he finally stopped", authorities said. "We did seize the bus, we've applied for a search warrant, and we'll be actively searching that bus".