The shooting happened at the Pablo Davis Elder Living Center at about 5:45 p.m. Sunday, The Detroit News reported.
The first victim, a 54-year-old woman, was shot and killed outside while she was hanging out with a friend.
"I didn't see the rifle until he got right on top of us," said Paul Fratangelo, who was with the first victim at the time of the shooting. "I said, 'Oh my God. ..." He said, 'Get on the ground and start praying.'"
The second victim, 65, was found dead in her apartment.
The suspect, 65, was arrested by police shortly after the shooting.
Police did not release the identities of the alleged gunman and two victims.
Will Staples, another resident of the senior living center, said the victims were close friends of the suspect's wife.
"Everyone knows everyone in here, but they were all good friends," Staples said. "People called them the Three Musketeers."