BROKEN ARROW, Okla. » One of two brothers charged in the stabbing deaths of his parents and three siblings in suburban Tulsa told police that plans for the attack were on a USB flash drive inside the family’s home, according to an affidavit for a search warrant.

The affidavit, filed Thursday in district court along with other police documents, doesn’t say which brother made the statement, only that he “spontaneously uttered” while being arrested that the plans were on the drive in a bedroom of the Broken Arrow home.

Eighteen-year-old Robert Bever and his 16-year-old brother, Michael Bever, are charged with first-degree murder in the July 22 attack. A judge has entered not-guilty pleas for them. Their defense attorneys couldn’t immediately be reached late Thursday for comment on the document.

The affidavit doesn’t offer any description about the alleged plans. But an investigator wrote that authorities would likely find evidence inside the home, including dark and bloodstained clothes, a mask and gloves, as well as electronic devices that could store “information on the planning and execution of a mass homicide.” They would also likely find “sharp-edged weapons,” such as knives, swords and machetes, the investigator wrote. Investigators also requested DNA evidence from the brothers.

Authorities have not commented on a possible motive.

Also Thursday, police released a summary of the 911 call from the early minutes of the attack at the home of David and April Bever and their seven children. It was released to reporters after a judge ruled a day earlier that the audio, which police had described as “gruesome,” should not be made public.

An account begins at 11:33 p.m., when a dispatcher notes, “Someone is attacking her family. I can’t get any further info.” The dispatcher then adds there was a male on the line who said “hello” before the line went dead. The log notes that there was “a lot of screaming in the background and I could hear someone trying to be quiet and crying.”

The dispatcher notes that the call was placed from a disconnected cellphone and the voice initially sounded like a young female. Police initially believed a girl made the call but now say it’s more likely the distress call was placed by one of two younger boys before both were killed.

The dispatcher called the home number for David Bever; someone picked up without speaking to the dispatcher, then hung up. The dispatcher retried the number and the voicemail switched on.

The first police officer arrived at the home seven minutes later, and within three minutes he had called for ambulances twice. At 11:44 p.m., he wanted another squad car because he had “3 down with stabbing.” The older brother was quickly named as a suspect: “Son/brother armed with knife.”

Around midnight, police combing through the house found one victim in a bedroom off the kitchen who was cold with no pulse and two small children in the bathroom, according to the transcript.

At 12:05 a.m. on July 23, officers gave the final tally: Five confirmed deaths and one injured 13-year-old girl. A 2-year-old sister wasn’t harmed.

Police dogs took about three minutes to track the brothers down to a wooded area near their home. Robert and Michael Bever were apprehended about a half-hour after the initial call.

Police said previously that they recovered knives and a small hatchet from the home. The records released Thursday used the term “severe laceration” to describe the victims’ injuries.

Records of service calls to the residents show that three years earlier, police went to the house to check a “drunk in public” call just before 2 a.m. The log doesn’t say who was drunk, and that call came two days after a suspicious person call.

Dozens of people on Thursday evening attended a memorial vigil at a Baptist church not far from the Bever home to honor the victims.

Attendees stood and cheered some of the police and firefighters who had responded to the scene and were at the service.

Local pastors prayed that family members of the victims would begin to heal. City officials pledged the killings wouldn’t define the city, which barely logs one homicide a year.

“Our community is in shock,” police chaplain Scott Keele said. “For many of us, we can barely wrap our heads around this event.”