(CBS News) WATERTOWN TOWNSHIP, Minn. -- Sheriff Jim Olson was going through daily police reports last month when he came across a familiar name: Chris Oberender. Olson had been a young detective when he met with Oberender in 1995.
At the time, "Chris was 14 years old and murdered his mother," Olson says. He killed his mother with a gun.
When he was 21, Oberender was released from a mental hospital. Under Minnesota law, he was banned from owning a gun. That's what troubled Olson about the police report he was reading.
"And I saw the pictures that he had of guns on his Facebook page," Olson says. "He can't have guns. Chris Oberender should not have guns."
Asked how a man like Oberender, who was convicted of murdering his mother with a gun, obtains a firearm, Olson responds, "I wish I had a good answer for that. I don't."
Oberender passed a background check in 2011 and obtained a Minnesota gun permit. Police found 15 guns in all at Oberender's house. They also discovered a letter Oberender recently wrote to his dead mother.
The letter read, in part, "I am so homicide. What is wrong with me? I think about killing all the time."
Olson says reading those words was "chilling."
He says Oberender passed a background check because sloppy file keeping by the courts left critical criminal information out of his legal record. There were no fingerprints or record from the court.
What was in the record was Oberender's forced commitment to the mental hospital.
"In this case, we were lucky," says Lucinda Jesson, the state's top mental health official. "No one was hurt through the good actions of local law enforcement."
Jesson told CBS News law enforcement would have found the mental hospital record if they'd checked.
"We have to be asked to run the match," she says. "That does not always happen. ... It's not automatic."
"We were not aware he was not in the system until New Year's Eve," Olson says. "I would call it providence."
Today, Oberender is in jail awaiting trial for illegal possession of firearms. State officials say they have incomplete records for 168,000 people from Minnesota who want to buy guns, and under the law, if the state cannot find complete records, it must issue a permit within seven days.