They knew the house far too well. It was where Christian Philip Oberender, then 14 years old, had murdered his mother in a shotgun ambush in the family rec room in 1995.

Now, 18 years later, Carver County Sheriff Jim Olson was sending his deputies back to the home where Oberender still lives. Just two days earlier, Olson had scanned the day's shift reports and froze when he tripped over Oberender's name. A scan of a Facebook page then showed firearms spread out like a child's trophies on a bed inside the home, along with notes about the Newtown, Conn., gunman who shot 20 children to death.

What Olson's deputies found in the home in Watertown Township was chilling: 13 guns, including semi-automatic rifles, an AK-47, a Tommy gun, assorted shotguns and handguns, including a .50-caliber Desert Eagle.

Even more disturbing was the letter Oberender had written recently to his late mother, Mary: "I am so homicide," it said in broken sentences. "I think about killing all the time. The monster want out. He only been out one time and someone die."

Today, Oberender sits in a Carver County jail cell on a charge of being a felon in possession of firearms. And Olson, who investigated the 1995 murder as a young detective, finds his investigators at the center of a case that exposes the dangerous loopholes in the nation's gun laws and Minnesota's system of criminal background checks.

Even though Oberender killed his mother with a firearm, even though he was committed to the state hospital in St. Peter as mentally ill and dangerous more than a decade ago, he was able to obtain a permit to purchase firearms last May. That piece of paper gave Oberender, now 32, the ability to walk into any licensed Minnesota retailer and buy any assault weapon or pistol on the rack.

Dozens of other Minnesotans judged by a court to be mentally ill have also found that designation no barrier to obtaining deadly weapons.

A Star Tribune review of state court records found case after case in which individuals deemed mentally ill in judicial proceedings later wound up in possession of guns and accused of violent crimes.

At least 84 people have been charged since 2000 with illegal gun possession or assault with a dangerous weapon even though they had previously been committed by a judge as mentally ill. Of that group, 29 were charged with multiple counts of weapons possession and nine were considered by a judge to be mentally ill and dangerous.

Additionally, the Minnesota Bureau of Criminal Apprehension (BCA) has more than 168,000 "suspense files" -- records on Minnesotans who have been arrested since 1990 but whose files are so incomplete that the state can't determine if they should have the right to buy guns.

"The system failed in this case," Olson said in an interview. "We are having discussions with the BCA to make sure there aren't similar things like this hanging out there."

Federal agents from the Bureau of Alcohol, Tobacco and Firearms are working with Olson's investigators to sort out which guns Oberender might have bought from retailers using a permit he should never have possessed.

No red flags

How did Christian Oberender succeed in obtaining a gun permit?

The answer lies in a combination of deceit on his part, failures in the state court system, and haphazard data collection by state agencies, according to interviews with law enforcement officials.

In Minnesota, a person seeking a permit to purchase an assault weapon or pistol must submit an application to the local police or sheriff's department. There, the background check process begins with a query of the BCA's system. If no disqualifications show up -- such as a violent criminal record or mental illness commitment -- the permit is granted.

No state permit is required to purchase a long rifle or a shotgun in Minnesota. Buyers going to a licensed retailer must pass a federal background check at the counter -- but those records can also be incomplete because they are supplied to the FBI by state agencies.

Minnesota's gun laws don't require an applicant to provide a fingerprint or a Social Security number to verify identity.

"This was one of our concerns during the 'Conceal and Carry' debate in Legislature 10 years ago and it was beaten down like everything else," said Heather Martens, executive director of Protect Minnesota, a gun violence prevention organization.

Martens said Oberender's case highlights the reluctance of lawmakers to tighten gun laws because they fear being accused of infringing on individual rights. "Public schoolteachers have to go through a complete background check, even including a fingerprint," Martens said. "For buyers of assault weapons and pistols, law enforcement currently has only seven days to verify the person's identity and criminal history -- otherwise, a permit is automatically granted. We should at least allow police enough time to verify the person's identity."

At the BCA, a spokesperson said the agency's database will catch closely matched names and aliases, but it would not snag a name like the one on Oberender's application.

In Oberender's case, the first glitch was that he simply transposed his first name and middle name on the gun permit application, apparently in an attempt to avoid recognition by the BCA's database.

Additionally, when Oberender applied for his permit, records show, he lied about his mental health history, a move that triggered no red flag in the computers -- the BCA's system doesn't contain any state commitment records of the mentally ill and dangerous.

"When we checked the record, there were no disqualifiers for a 'Philip Christian Oberender,'" said Carver Deputy Jason Kamerud.

Last week, investigators also learned that Oberender's juvenile record -- where the murder of his mother is recorded -- had not been attached to his criminal history at the BCA. Carver investigators are still puzzled over that.

In a statement, BCA spokesperson Jill Oliveira said, "There were no data submitted to the BCA about this individual; without it there can be no record."

Loopholes

The state's criminal background system appears to contain another loophole for violent felons and persons found mentally ill and dangerous who want to escape scrutiny. Under state law, a person's juvenile record is deleted from the BCA's database when the individual turns 28 unless a judge says otherwise, Oliveira said. As a result, a person with a violent juvenile record -- like Oberender -- might still qualify to buy a gun if there were no felonies on his adult record.

State law requires the Minnesota Department of Human Services (DHS) to provide local law enforcement agencies with records of people who have been committed to institutional care for mental illness, if the applicant gives consent. But in general, the BCA said, a court order for civil commitment is classified as private data and is not available to the BCA.

"There is no way that BCA can have DHS's commitment data," Oliveira said in a statement. In addition, about half of those committed by a court are directed to community providers, not state facilities, thus leaving it to the courts, not DHS, to ensure that the records are sent.

It's unclear whether Oberender's mental health history was ever entered into any background check database.

In late 2011, DHS tried to streamline the process, opening an electronic portal for background checks used by law enforcement officials. Last year an estimated 32,000 checks were conducted, and about 500 people were flagged as potential risks. When that happens, the agency provides law enforcement officials with a deeper check on people who could be disqualified.

DHS also checks the state Supreme Court information system, currently the most accurate record of commitments, the agency said in a statement. "However," it added, "without additional identifying information, it may be difficult to determine whether someone with a common name matches an entry in the system."

'Want to hurt people'

Oberender received three years of intensive treatment for his mental illness as a juvenile, but in late 1998 was ordered committed as "mentally ill and dangerous" to the St. Peter state hospital. Mental health professionals wrote in court findings that they believed there was "a substantial likelihood that Oberender will engage in acts capable of inflicting serious physical harm to another." There are apparently no public records of when he was released from St. Peter. In a 2003 interview with the Star Tribune, Oberender said he spent a year in a halfway house after his release and believed he was turning his life around thanks to "all kinds of treatment."

The felony charge he now faces could put him in prison for up to five years, or it could lead a judge to send him back to St. Peter for psychiatric care.

Before his arrest, Oberender had been working as a skilled mechanic at a local sanitation hauling company.

David Peterson, a co-worker and friend, said he believes his friend must have been living two lives.

The two often spent time shooting guns behind Oberender's home, at targets ranging from old television sets to junk cars and pop cans, all the while critiquing each weapon, he said. He said that Oberender told him that he bought most of his guns at two licensed retail stores in the area and that the weapons were all registered.

Oberender, he said, rarely mentioned his past, sharing only brief snippets about the murder.

Still, Peterson said he felt so comfortable with Oberender that he invited him to his home for social occasions and was planning on setting him up with a date. "He is an excellent, great friend," Peterson said.

Then there was the other life, the one where a self-described "monster" lived inside the quiet young man.

"I think about killing all the time," Oberender wrote. "Why god do I feel like this? The monster want to hurt people. Guns are too fast. The monster want it to be slow and painful. There is so much pain in my heart and soul. Me want other to feel it."

Sheriff Olson read the letter after his investigators inventoried their evidence.

"It was chilling," he said.

Paul McEnroe • 612-673-1745