The two Oklahoma brothers who allegedly stabbed five family members to death last week reportedly had planned the attack for a long time and wanted to kill more people.

Sources told News on 6 Robert Bever and his 16-year-old brother, of Broken Arrow, wanted to kill their family first because they considered them to be easier targets. The station reports the brothers then wanted to attack other people because they considered them harder targets.

News on 6 also reported that 3,000 rounds of ammunition were delivered to the home days after the stabbings took place. Bever, 18, and his brother were planning on using the ammo to commit an atrocity that would rival that of the 1999 Columbine High School shooting in Colorado, the station reported.

On Monday, the Oklahoma medical examiner’s office confirmed the couple and three of their children found dead inside the home all died from “multiple sharp-force injuries.”

The killings of David Bever, 52, his wife April Bever, 44, and siblings Daniel Bever, 12, Christopher Bever, 7, and Victoria Bever, 5, have been classified as homicides, said office spokeswoman Amy Elliott. The final autopsy reports have not been released, Elliott said.

Robert Bever is accused in a booking document of five counts of first-degree murder and a count of aggravated assault in the attack. His 16-year-old brother is being charged as an adult in the case.

Broken Arrow City Attorney Beth Anne Wilkening said in a statement on Tuesday police will release the 911 call made from inside the home next Tuesday.

Authorities initially said the call, described by Broken Arrow Police Sgt. Thomas Cooper as "gruesome," would be released Monday, but an assistant to the city attorney then indicated that it wouldn't be because it's part of the investigation into the deaths of five members of the Bever family.

Wilkening said the release was delayed because a prosecutor was concerned the provision of certain records to reporters “could impact the prosecutorial integrity of the case."

Cooper had previously described the nature of the call: the caller reports that his brother is attacking the family before the caller and dispatcher have a short exchange about the location of the home.

"They're able to confirm the location, and then it basically goes to an open line for a little while and you can hear a struggle there and then it disconnects," Cooper said. "It's fairly short, but it's gruesome. Obviously the entire crime is gruesome, and the 911 call is just as bad."

A media law expert and advocate for public access to records had called on law enforcement Tuesday to release the audio, saying "the investigation doesn't begin until the 911 call" is made.

"If there's a gray area, disclosure should be favored over withholding," said Joey Senat, an associate professor at the Oklahoma State University School of Media and Strategic Communications.

The two teens are scheduled to be arraigned in court on Aug. 3, at which time a plea is expected to be entered on their behalf and a preliminary hearing date will be scheduled.

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The Associated Press contributed to this report.