A man opened fire aboard a moving Atlanta metro train on Thursday, killing one man and wounding three other passengers before the suspected gunman was arrested at the next station, a police spokesman said.The gunfire erupted aboard a Blue Line train at about 4:30 p.m. shortly after it left a station on the city's west side, Joseph Dorsey, deputy chief of the MARTA police, said at a news conference. MARTA is the Metropolitan Atlanta Rapid Transit Authority."As the train was in motion, the suspect fired several shots toward the victims," Dorsey said.The three people who were wounded are expected to survive, Dorsey said. A fifth person suffered an ankle injury as passengers scrambled away from the gunman.All the victims, as well as the suspected gunman, were in their 30s, Dorsey said.The shooting was "targeted, but isolated," MARTA's Police Chief Wanda Dunham said, according to the Atlanta Journal Constitution newspaper.Police detained the suspected gunman at the train's next stop, West Lake Station, and recovered a weapon, Dorsey said. He gave no information about a possible motive and said the shooting was under investigation.A man who was in the train car told Atlanta's Fox 5 television that a man wearing a hat sat next to another passenger, his head bobbing. The man then got up and walked to the back of the car."And after that, heard shots, hit the deck, and just saw some shoes walk past and that's it," said the man, who was not identified.Cellphone video shot by a bystander and carried on the Fox station's Facebook page showed a woman and another person lying on the floor of a train car as passengers bent over them.The transit agency said the station had been temporarily closed.