How Does Someone With Repeated Psychiatric Hospitalizations, Drug Arrests and Jail Time, Buy A Gun?

Some reporters and perhaps even federal investigators are all asking the same question. How did John Patrick Bedell buy a gun if as reports indicate, he had been repeatedly committed to mental institutions for bipolar disorder and spent 30 days in jail for a resisting arrest conviction? How would he have been able to pass the background check which one would imagine would have indicated any psychiatric hospitalization and also his several arrests, jail time and violations of probation? Not only that, but according to a missing person report his family filed with the San Benito Sheriffs Department, he had been detained by police for a mental evaluation only a few days before he allegedly made a $600 purchase at a shooting range. The shooting range purchase on January 10th was discovered by his mother who had come across "some information -- either from an e-mail received from a company, or an online posting on a bank account or something."

According to a website on the Firearm Background Check, it seems he actually may have been able to purchase a weapon if his psychiatric hospitalization had been voluntary, and since his conviction was not for a felony, and the drug charges were dismissed.

But then how does that correspond to accounts like this one in The Washington Post where the shooter's brother claims he failed a background check near Sacramento when he tried to purchase a gun? According to the article, the mother of the shooter claims he later made a purchase at a Washington area gun shop. Could he have been more successful there? And didn't the mother already say he spent $600 at the shooting range in Sacramento?

Update: It seems that his guilty plea for marijuana cultivation and also his arrest on suspicion of driving while under the influence of marijuana are also red flags that should have come up in his background check since "unlawful drug users" is a reason for rejection.