Denver Police Cmdr. Ron Saunier said law enforcement officials don't expect to make any more arrests at this time, but will still investigate the crime and execute search warrants as needed, KUSA-TV, Denver, reported.
Police said federal agents assisted in the arrest of Dexter Lewis, 22, Joseph Hill, 27, and Lynell Hill, 24, late Wednesday.
Saunier said police believe Fero's Bar & Grill was the scene of a robbery gone awry and that the suspects set the fire to hide their crime.
The three suspects likely will face five first-degree murder, five felony murder and other charges including arson and felony robbery, KUSA said.
Police said Young Fero, 63, the owner of Fero's Bar & Grill, and four others were killed sometime around last call before the bar was set on fire. The other victims were identified as Daria M. Pohl, 22, Kellene Fallon, 45, and Tereasa Beesley, 45, all of Denver, and Ross Richter, 29, whose hometown was not reported.
Saunier said detectives believe the victims were killed before the fire started, saying without elaboration the bodies exhibited signs of trauma.
"The business had obviously been set on fire or arson," Saunier said. "I'm guessing to mask the homicide that occurred inside at this point."
A memorial in front of Fero's grew as customers and friends dropped by to pay respects Wednesday. Many told KUSA they considered the bar a second home and its owner a second mother.
"This was a place where we all gathered and we all were a family," employee Jolene Frazzini. "We'll miss her."