"He made it past the door and then he got ambushed. ... Once he passes that door, he gets shot, and that first shot is a fatal wound," Lehn said, noting the bullet hit Bradway in an area that wasn't covered by his bulletproof vest.
He said the 41-year-old Bradway, who was pronounced dead at an Indianapolis hospital, had little time to react.
A second officer rushed in and exchanged multiple shots with the gunman, eventually killing him. The Marion County Coroner's Office identified the alleged gunman as 24-year-old Steven Byrdo. Lehn said about 15 shots were fired and that Bradway's gun discharged, but it's unclear how many he got off.
"There are bullet holes everywhere," Lehn told The Indianapolis Star.
The woman, whom Lehn said was an ex-girlfriend of Byrdo, and her 11-month-old child weren't harmed, Lehn said. The child is now in the care of child protective services, said police spokesman Officer Kendale Adams.
Indiana Department of Correction records show Byrdo had felony drug convictions in 2011 and 2013 and had been released from prison in June after serving a sentence for a cocaine-dealing conviction.
Officers were dispatched to the apartment complex on the city's northwest side about 2 a.m. after someone called 911 to report a disturbance.
Bradway, who was married with a teenage son and daughter, was a five-year veteran of the department, according to police. He was a native of the northern Indiana town of Nappanee.
Police Chief Rick Hite asked the public to pray for Bradway's family.
"He entered an apartment to save the life of a woman who was being assaulted and in turn gave his life," Hite told reporters. "Blessed are the peacemakers."
The department said Bradway was a highly decorated officer who had received its Medal of Bravery in February 2012.
A few dozen police squad cars escorted a vehicle carrying Bradway's body as it left the hospital on its way to the coroner's office. His police cruiser was placed outside the district office Friday afternoon and adorned with flowers.
Adams said Bradway had helped with relief efforts in the aftermath of the deadly May tornado in Moore, Okla. Bradway's wife, Jamie, wrote in the June issue of the city's Department of Public Safety newsletter that she and her husband helped collect supplies for pets displaced or found wandering after the tornado.
The couple took 28 pet crates, hundreds of pounds of dog and cat food, leashes, water bowls, animal toys and other items to Moore's animal shelter, she wrote. They were on hand when a family was happily reunited with their dog.
The shooting prompted Indianapolis Mayor Greg Ballard to cut short a trip to Germany for a business summit. In a statement, the mayor said Bradway "gave his life protecting the people of our community by charging ahead to confront the unknown."
Bradway is the first Indianapolis police officer killed in the line of duty since Officer David Moore was shot during a traffic stop on Jan. 23, 2011. He died three days later.