NILES, Mich. (WLS) -- A suspect is in custody after four people were stabbed on board an Amtrak train in southwestern Michigan Friday evening, police said. Three people and the train's conductor were injured in the incident in Niles, Mich.Police met the train at the Niles station after an Amtrak conductor called to report a man acting erratically on board. While the train was stopped, the suspect pulled out a knife and started attacking several people, including the conductor."At 7 o'clock this evening our dispatch center received a call, I believe, from the Amtrak center in Chicago advising that the Amtrak train had an individual on board that was acting a little odd and becoming agitated and they wanted the police to come up. And when our officers arrived, the subject had assaulted four individuals on the train with a knife," said Chief Jim Millen, Niles Police Department.Police boarded the train and confronted the suspect, who they say then threatened officers with a knife. They used a stun gun on him and handcuffed him.Police have not identified the suspect at this point, but said he is a 44-year-old man from Saginaw, Mich., who boarded the train in Chicago."I dove out of an open door of the train, so I was standing by the track when everybody was being brought out, and yeah, there was some people brought out in pretty bad shape. I don't know how they are doing now," said Tyler Vandermolen, a witness.Amtrak said in a statement Friday night that the incident took place on board Train #364 at the Niles Train Station. The train was operating on the Blue Water Service line, and was en route from Chicago to Port Huron, Mich.The victims include three men and one woman. One person was injured quite seriously, while the others sustained non-life-threatening injuries.Amtrak said 172 passengers were on board the train. The train will continue to Port Huron after police have finished investigating.Niles is located in Berrien County, about 11 miles north of South Bend, Ind.