BROKEN ARROW, Oklahoma - What looks like such a normal Broken Arrow home is the location of the most gruesome crime the city has seen.

A hatchet was just one of the weapons police said 18-year-old Robert Bever and his 16-year-old brother used to stab six of their family members.

Less than 24 hours into the investigation, officers are haunted by Bever's smirk, according to Corporal Leon Calhoun, with Broken Arrow Police.

"Kinda hard for a rational person to even comprehend, that someone could do something this horrific and not have any remorse afterwards," he said.

Police said someone in the house dialed 911 around 11:30 Wednesday night but didn't say a word to dispatchers; and when police got to the house all they heard was moaning.

Investigators found five bodies - the brothers' parents, David and April Bever, their 5-year-old sister and their 12 and 7-year-old brothers.

The brothers' 13-year-old sister survived and is now recovering after surgery; their 2-year-old sister was the only one left unharmed.

Neighbors, like John Alexander, are in shock, saying the family kept to themselves – the father worked from home, the kids were home-schooled and not allowed to play with neighbor kids.

"It's tragic the way it happened. Even worse with children involved. You hate to see it anywhere," Alexander said.

The family had just founded a nonprofit to help parents of premature babies; their 2-year-old daughter, the only one not stabbed, was born prematurely.

Neighbor Maggie Jacobson said she talked to the mom, April, about the baby.

"She was born early, so I talked to April a lot about that stuff. She had some medical issues and stuff," she said.

Investigators said the 2-year-old is now with relatives.

The brothers are in the Broken Arrow Jail where they'll be questioned extensively.

Investigators also want to talk to the 13-year-old girl but said, because she’s been through unimaginable trauma, they're taking their time.

Police said they want to know more about the brothers' motive, but said they'll wait until Friday to release more information.