NILES, Mich. » A man wielding a knife stabbed four people aboard a passenger train Friday, including an Amtrak employee, police said.

The suspect was in custody Friday night and police said all four wounded people were taken to hospitals with varying degrees of injuries. Police were still trying to figure out what motivated the attack.

The train was traveling from Chicago to Port Huron, Michigan, and the attack happened at Niles, Michigan, about 100 miles east of Chicago.

Passenger Caitlin Cipri told the South Bend Tribune in Indiana that she was packing her things to get off the train when she heard screaming. She initially thought the suspect was punching a passenger until she saw the butt of a knife. Cipri said she then saw the man stab two other people.

"It was terrifying and you don’t think something like that is going to happen to you," Cipri said. "It’s terrifying that things like this happen."

Niles Police Chief Jim Millin said police dispatch received a call from the train around 7 p.m. from someone reporting a suspicious person. When police arrived at the Niles train station, the attack was already underway, Millin said. Police stormed the train and used a Taser on the suspect before taking him into custody.

Police say the 44-year-old suspect is from Saginaw, Michigan.

Amtrak spokeswoman Kimberly Woods said the Amtrak Police Department is helping Niles city police with its investigation. She said the company arranged alternate transportation for 172 passengers.