A 16-year-old carried out a shooting at Silver Rail Elementary School in Bend, Oregon, last week, killing three children and a teacher before he was fatally shot by a student's parent. Another child and a teacher were injured, officials said. Bend Police Chief Mike Krantz said a pump-action shotgun was found near the suspect, who had about 44 remaining rounds of ammunition.

Investigators are examining how the teenager obtained the firearm and ammunition, which Krantz described as part of an "active criminal investigation." A senior law enforcement official briefed on the case told CNN the gun had been purchased by the teen's mother. The official said the parents were interviewed and cooperated, and that a search warrant was executed at the family's home on Thursday, with computers and other electronics taken. Additional search warrants have been obtained to gain access to further records.

Oregon law generally prohibits anyone under 18 from possessing a firearm, with exceptions for certain long guns transferred by a parent or used temporarily for hunting or target practice. Whether those exceptions apply, and what the parents knew about any risk, are expected to be central questions. CNN law enforcement analyst Andrew McCabe said the case could lead to criminal charges against the parents, as in other recent cases, and CNN analyst Juliette Kayyem said the inquiry would likely focus on how the teen accessed guns and what his parents knew.

Recent prosecutions elsewhere provide precedent. In Michigan, James and Jennifer Crumbley were convicted of manslaughter and sentenced to 10 to 15 years in prison after their 14-year-old son Ethan carried out a school shooting. In Georgia, Colin Gray was convicted of murder and sentenced to 15 years after his 14-year-old son Colt carried out a school shooting. In Wisconsin, Jeffrey Rupnow, 44, has pleaded not guilty to three felony charges for allegedly allowing his 15-year-old daughter access to firearms, with trial set for March.

Prosecutors in such cases have said the goal is to push gun-owning parents to secure firearms and prevent future school shootings. No charges have been announced in Oregon, and the investigation is in its early stages. Authorities have not said when decisions on potential charges will be made.