Investigators were questioning several witnesses and possible suspects in connection with the execution-style slaying of two DeKalb County police officers, a department official told FOXNews.com.
Hours after Police Chief Terrell Bolton vowed to find the killers "before sundown," detectives had brought in several people who saw the shootings, might know something about them or could have otherwise been involved, said department director Keisha Williams.
"We're questioning a lot of witnesses and potential suspects and people who may have heard the shots," Williams said. No specific person or persons of interest have yet been identified, she added.
A reward that by Wednesday evening was at $55,000 and growing has been offered for information leading to the capture of suspects in the murder of off-duty DeKalb County officers Ricky Bryant Jr., 26, and Eric Barker, 33, according to Williams.
Bryant and Barker were shot early Wednesday morning in an apparent ambush on an apartment complex.
The fallen officers "were struck down by evil," Bolton said in an afternoon news conference.
Williams said police believe there are at least two suspects, though there could be a third. No description has been offered.
DeKalb authorities said they're using all available resources in the manhunt and "will not rest" until those responsible are caught.
"This is a must-solve crime," Bolton told reporters. "It is a crime that must be solved quickly."
He said investigators know there are witnesses to the killings and "we want them to come forward."
The chief held up photographs of Bryant, a two-year veteran of the department, and Barker, who worked there for four years. Both are married with four children, he said.
"Bottom line: We lost two police officers for nothing," the chief said at the Wednesday afternoon press conference. "They clearly didn't have the advantage, or we wouldn't be here. Obviously something terrible happened."
Earlier Wednesday, Bolton had a message for the gunmen: "If I were you, I'd turn myself in. The sun's coming up. Before sundown, we're gonna find you."
But as the day wore on, Williams said she didn't know when the murder suspects would be caught.
"I can't judge when we're going to make an arrest," she told FOXNews.com. "It's an extensive manhunt. I hope we get them before sundown, but I can't make any predictions."
The officers were gunned down early Wednesday in an area known to have a high rate of crime, during an apparent ambush at the Glenwood Gardens apartment complex. The two were working as security guards at the complex and were investigating a suspicious person there when shots rang out, Bolton told The Associated Press earlier Wednesday.
Authorities were initially seeking two males seen running from the scene. Police were using dogs and a helicopter to aid in the manhunt.
"We've got every able body looking for them," Bolton told the AP.
Police were called to the site of the shootings at about 12:40 a.m. Wednesday, according to Bolton. One officer was dead at the scene; the other was pronounced dead at Grady Memorial Hospital in Atlanta, the chief said.
Bolton said the shooting looked like an ambush.
"It just appeared that they were gunned down without a chance," he said. "It's a challenging day for us. Today's act of senseless violence is a display of what we're seeing around the country where people will shoot down a police officer without regard to any repercussions."
Schools were locked down during the investigation in the area about 6 miles east of downtown Atlanta.
Patreka Anderson, a resident of the complex, said she was awakened by the gunshots but did not think anything of it because the neighborhood around the Glenwood Gardens apartment complex is a high-crime area with a lot of drug activity and prostitution.
"We always hear shooting," she said. "I didn't think that was any big deal."
Teofil Taut, who said he has owned the 176-unit complex for about two years and lives in one of the buildings, said he hired police as part-time security officers in December to keep homeless people from breaking into the apartments.
Another resident, nurse's assistant LaShawn Corbin, said she is considering moving, even if it means paying more for an apartment.
"We don't expect the people who try to protect us to be hurt so seriously," she said. Corbin said she would fear leaving her children there "because the person who did it has no conscience for human life."
Anyone with any information in the case can call Crime Stoppers at 404.577.TIPS.
FOX News' Catherine Donaldson-Evans and The Associated Press contributed to this report.