The family of 22-year-old Jared Loughner reportedly returned home from a grocery shopping trip on Saturday to unthinkable news: Their son had allegedly shot Rep. Gabrielle Giffords (D-Ariz.) and 19 others, killing six.

The family remained silent, barricaded from the press in their Tucson, Ariz., home, for days after the shooting. On Tuesday (Jan. 11), they released a brief statement expressing sympathy for the victims' families and asking for privacy.

"There are no words that can possibly express how we feel," the statement read, in part. "We wish that there were so we can make you feel better. We don't understand why this happened."

Psychologists say the parents must be experiencing devastating grief and perhaps guilt over the son's actions. But there is no roadmap for the Loughners' experience, and only a few parents have stood in their shoes.

"We run into this problem of generalizing from the available research to something that is so unique like this," Frank Farley, a psychologist at Temple University in Pennsylvania and a former president of the American Psychological Association, told LiveScience. "The kind of stuff that gets published in the field of family psychology, most of it doesn't come close to being comparable to this." [Read Insanity, Rhetoric and Violence: No Easy Answers]

Private grief

Families such as the Loughners often choose to avoid the public view. The families of Columbine shooters Eric Harris and Dylan Klebold kept almost completely silent for years. It wasn't until 2004 — five years after the tragedy — that the Klebolds spoke to the media in any depth. They told New York Times columnist David Brooks that they had no inkling of their son's intentions. Nor did they have time to grieve for their child, said Dylan's mother, Susan Klebold. (Both Harris and Klebold committed suicide after killing 13 and wounding two dozen more in their high school.) In 2009, Susan Klebold, Dylan's mom, wrote an article in O Magazine describing herself as "insane with sorrow" for months after the shooting.

"It was impossible to believe that someone I had raised could cause so much suffering," Klebold wrote. As she blamed herself for not seeing that her son needed help, the public blamed her and her husband for raising a "monster," she recalled. [Read: What Makes a Psychopath?]

The Harris family has not spoken publicly about their experience.  

After the 2007 massacre of 32 people at Virginia Tech, Sun-Kyung Cho, the sister of shooter Seung-Hui Cho, released a statement apologizing for the devastation caused by her brother.

"We never could have envisioned that he was capable of so much violence," Cho wrote. "He has made the world weep. We are living a nightmare."

A year later, the Washington Post reported that family members continued to isolate themselves even from relatives.

Struggling to cope

Likewise, Loughner's parents may be struggling to cope with not only the impact of the shooting but the sudden notoriety of the family, Farley said.

The shooting "has brought about a response by the president of the United States and the speaker of the house," Farley said. For the parents, "that [notoriety] is so extreme that maybe they're just having problems handling it all… Their silence maybe speaks volumes about how heavily this has impacted them."

Little is known about the family except for a few descriptions by neighbors. Many say the Loughners have long been isolated. One neighbor, Wayne Smith, told reporters that the couple is "hurting" and "can't talk without breaking down."

Smith said the Loughners told him they have no idea why their son would shoot anyone. He described them as feeling guilty and devastated.

"There's probably going to be a lot of guilt," said Priscilla Dass-Brailsford, a trauma expert in the department of psychiatry at Georgetown University Medical Center. "They're probably going to second-guess themselves."

No one knows how aware the Loughners were of their son's apparent mental instability. Even if they did see signs, it may have been difficult to get him help, Dass-Brailsford said.

"When someone is older than 18, it gets really tricky," she said. "The person has to really be doing something egregious for them to get the help of the state."

Forcing an unwilling adult into treatment means turning to the courts, a process that can be difficult for families.

"People feel failure as parents, and yeah, it's a tragedy when that has to be done," Dass-Brailsford said.

After the fact, community support and professional help can pull a family through a tragedy, Dass-Brailsford said, but it's unlikely the family will ever truly leave the experience behind.

"There's going to be a trial, there's going to be all the news media when he goes to trial. His parents may be brought in to testify. It's going to be ongoing, and long," Dass-Brailsford said. "For them, the tragedy is only beginning."

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You can follow LiveScience Senior Writer Stephanie Pappas on Twitter @sipappas.