Killed were two adults and three children. A girl was critically injured. Two suspects --16- and 18-year-old brothers, both related to the victims -- ran out the door as police arrived, officials said.

The teens didn't remain on the loose for long. They were tracked down with the help of a police dog.

It was not immediately clear what charges the teens may face or what spurred the gruesome crime.

Whatever the motivation, the episode has shaken citizens in Broken Arrow, a Tulsa suburb of about 100,000 people that typically has one or two homicides a year, not five in one day.

"A crime like this is unprecedented for our area, just given our safe community," Broken Arrow police Sgt. Thomas Cooper told CNN affiliate KJRH . "Unfortunately, it is a family that was destroyed over a crime, and we have to remember those victims as well as those officers and initial responders."

Police: Officers risked lives pulling out victims

Authorities got their first hint of trouble about 11:30 p.m. Wednesday in the form of a 911 call placed from a home in what Broken Arrow Police Cpl. Leon Calhoun called a low-crime and "very middle-class" neigborhood.

Yet that didn't mean they knew what to expect. The 911 call came from an open line, Cooper explained to CNN, meaning it went through but there was no conversation with the dispatcher.

Two officers arrived, knocked on the door, but got no answer. But they did hear moaning and forced their way in, according to Calhoun.

It was a nightmare. The officers saw a wounded 13-year-old girl and pulled her out to safety. Then they took out two more victims.

The officers risked their lives in the process, said Calhoun, because they had no idea if a killer or killers lurked nearby.

The final toll became clear only after authorities canvassed the entire single-family home. Two adults and three juveniles were dead, while two more people -- the 13-year-old girl and a 2-year-old girl, who was unharmed -- were alive.

Several blade-type weapons were found in the house, including a small hatchet, Calhoun said, "which would tell you that the scene was pretty gory."

Police identified two of the victims on Thursday: David Bever, 52, and April Bever, 44. The other victims were a 5-year-old female, a 7-year-old male and a 12-year-old male, Calhoun said.

Toddler in protective custody; 13-year-old in hospital

As to those responsible, Cooper told KJRH, "It appears that the two suspects fled out the door sometime during our arrival."

Police were soon on their trail, including a K-9 team that followed the teens into a wooded area behind the home where they were caught.

Broken Arrow police identified one of the suspects as Robert Bever, 18. The juvenile sibling was not identified.

No charges had been filed by Thursday night. If they are, Bever would face them as an adult, Cooper said.

It was unknown Thursday night whether he has an attorney.

The suspects, who are brothers, lived at the same Broken Arrow home as their victims. It's not clear if and when they'll appear in court and what charges they'll face, though Calhoun said five murder counts are a possibility.

As to their motivation, planning, and each one's role -- including whether one might have carried out the killings, while the other had a more passive role -- those are all things investigators are trying to figure out, said Calhoun.

Surviving family members might shed some light, but they've proven difficult to find. The two adult victims are believed to be the parents of the juveniles and suspects, according to Calhoun. And one challenge is that the family has moved around a lot, according to the Broken Arrow police corporal.

The one person without any injuries is a toddler and in state protective custody.

The 13-year-old girl was in critical condition Thursday morning at a nearby hospital. Calhoun said investigators want her condition to improve before they talk to her, though they think she'll be vital to the case.

We are "expecting the 13-year-old to help a lot," he said.