Lt. Chris Bailey said two officers responded to a report of shots fired near the intersection of 34th Street and Forest Manor Avenue at 9:24 p.m.
Four minutes later, at 9:28 p.m., the call went to dispatchers that an officer was down.
Renn and another officer encountered a man later identified as Major Davis Jr., 25, in an alley nearby. At that point, gunfire erupted, Bailey said.
Witnesses in the neighborhood told RTV6 they heard yelling, then gunshots.
One woman said she saw Davis with a gun just before shots were fired.
"I saw everybody outside around the house, and a girl was up on the guy who had the gun, and she was yelling and stuff like that," the woman said. "And I guess she didn't want him to shoot or whatever, but he had it like that, behind his leg, and he was probably ready to do something."
Davis was listed in critical condition and underwent surgery at Eskenazi Hospital. He is expected to be charged with murder.
Renn's family members gathered at the hospital, along with Mayor Greg Ballard, Marion County Public Safety Director Troy Riggs and IMPD Chief Rick Hite, in the immediate aftermath of the shooting.
"This is obviously a very difficult thing to accept," Ballard said in a news conference shortly after Renn's death was announced. "We'll work through this, but right now, this is a time for grieving."
"The city of Indianapolis was attacked tonight," Riggs said. "The officer wears a uniform that represents the best the city has to offer."
"Our officers responded to a report of shots fired, and someone saw fit to welcome us with an assault weapon," Hite said. "Major Davis has major issues, obviously. Where he got off track, we'll probably find out at a court date, but he had no right to take a fine officer's life."
Renn joined the department in December of 1993, and he worked as a street patrol officer his entire career.
Renn was awarded the Medal of Bravery in 2003, and he received a Letter of Commendation in 2012 for his work during the 2011 Indiana State Fair stage rigging collapse.
Thirty-one IMPD officers have been involved in violent confrontations within the last nine months.
"Tonight, and the next couple of days, it would be nice if the community would focus on the police officer and his family," said Rick Snyder, vice-president of the Indianapolis Fraternal Order of Police.
Watch the video below to see Renn being awarded the Medal of Bravery in 2003: