Dearborn police Chief Ron Deziel said the shootout occurred when police and FBI agents tried to serve an arrest warrant on Commit Rowson, 22, of Detroit at a Red Roof Inn.
Deziel said that as the agents tried to enter the room to question Rowson, he began shooting at the officers. No officers were shot, he said.
Rowson was killed in the gunfire exchange that began about 1:30 p.m., said Joseph Martinolich, FBI special agent in charge of the Detroit division.
Police on Sunday issued the arrest warrant for Rowson in the Nov. 13 armored car robbery that left a guard dead.
A Michigan National Bank guard, Daniel Hollie, 23, was arrested on Friday in the robbery and shooting. Hollie and Rowson were cousins, police said.
Hollie was arraigned on first-degree murder and other charges in the death of his security guard partner, Matthew Girardin, outside a Michigan National Bank branch in Dearborn, Deziel said.
Funeral services were held Saturday for Girardin, 29, of Garden City, who died at the scene.
Police had not recovered the $1.2 million stolen in the robbery.
Martinolich refused to say if the money was in the motel room. He said another person had been in the room with Rowson, but left before the shootout.
The person was being questioned by authorities, but was not under arrest.
Following the shootout, police surrounded the motel for about three hours not knowing whether Rowson was dead or hiding. Police tried to establish communications with Rowson. His mother was allowed to try to talk to him over a bullhorn.
About 4:15 p.m. a special weapons and tactics team went into the room and found the suspect dead, Martinolich said.
"We approached it as a barricaded gunman situation," he said.
Hollie was being held in the Wayne County Jail.
A preliminary hearing was not immediately scheduled. If convicted of first-degree murder, he would face mandatory life imprisonment without parole.