what the parents knew about the potential risks to others.

 I think this investigation will head the same way,  said CNN national security analyst Juliette Kayyem.  How did he get access to guns? What did the parents know? 

Where the Oregon investigation stands

In the Bend school shooting at Silver Rail Elementary School, the armed 16-year-old shooter killed three children and a teacher before he was fatally shot by a student's parent. Another child and teacher also were injured, officials said.

A pump-action shotgun was found near the gunman, who had about 44 remaining rounds of ammunition, Krantz said.

The gun had been purchased by the teen's mother, a senior law enforcement official briefed on the investigation told CNN.

The firearm used in the shooting was purchased legally, police said Wednesday, adding:  We are not sharing further information about the firearm at this time. 

Per Oregon law, it's illegal for a juvenile to possess a firearm but there are exceptions for certain long guns if the firearm was transferred by their parent or is used temporarily for hunting or target practice.

The shooter's parents were interviewed and were cooperative, a senior law enforcement official told CNN.

A search warrant was executed at the shooter's house on Thursday and computers and other electronics were taken, the source said.

Detectives served search warrants on the attacker's electronic devices and his social media accounts  on a variety of platforms,  Bend police said Wednesday.  That work continues, and it takes time. 

The shooter, Griffin J. John II, was a former special needs student at the school, police said. His mother spoke in 2020 with CNN affiliate KTVZ about his special needs and his enrollment in a program described as serving children with  intensive behavioral and social skills challenges. 

 I think it will be great for my son to get the help that he needs from the skilled teachers that he needs to get it from,  she told the station.

The shooter's mother spoke briefly with CNN off camera from her balcony on Friday. She said there were no warning signs and declined to comment on how her son got access to the gun.

 I'm so sorry, I wish I could have done something. I'm sorry for their loss,  she told CNN.

How the Michigan and Georgia cases unfolded

The criminal cases against the Crumbleys in Michigan and Colin Gray in Georgia featured similar allegations: An unsecured firearm and inattentive parents.

In each situation, a parent purchased a gun for their teenage son as a Christmas gift and left the firearm unsecured. The parents also allegedly knew their son had mental health problems and was a threat to others but did not properly address the issues by putting him into counseling or therapy.

Prosecutors argued the parents' actions represented  criminal negligence  - and the juries agreed.

For example, in Gray's trial, police had visited his home a year prior to the school shooting to investigate an online threat to shoot up a school. Colt Gray denied posting the threat and law enforcement was ultimately unable to substantiate the tip.

Colin Gray bought his son an AR-15-style rifle later that year. He testified he sometimes allowed his son to keep the rifle in his bedroom, and left other weapons and ammo lying around the house.

His defense attorney said he tried his best to help his son but simply didn't have warning about his violent plans. But prosecutors argued he acted negligently by buying a gun and ignoring warnings of the potential risk to others.

 This was a trial about this defendant's actions, his choices and his responsibility,  Barrow County District Attorney Brad Smith said.

In the Oregon case, there are more questions than answers at this point. How did the 16-year-old get access to the firearm and ammo? What did the parents know of their son's mental health issues and the potential threat he posed to others? Were there warning signs ahead of time, and what did people around him do about them?

Simply buying a gun for a child is not illegal on its own, legal experts said.

 The purchase, per se, is not necessarily improper,  said Katherine Schweit, a former Chicago prosecutor and FBI special agent.

McCabe said investigators will be looking for more than just a purchase history.

 They'll need evidence, actual proof that the parent knew that, let's say, the minor was in a vulnerable state. And the parent, despite knowing that, basically gave the minor access to the firearm, knowing that they might be in a vulnerable position,  he said.

 Those are all hard things to prove after the fact. So we'll have to see what comes out of the investigation.