WASHINGTON: United States (US) authorities in Pakistan could have sought ─ but did not ─ a full background security investigation of San Bernardino shooter Tashfeen Malik before granting her a visa to enter the country in 2014, according to a US official familiar with the matter.

Consular officials in American embassies overseas can ask US security agencies in Washington to produce a "Security Advisory Opinion", or SAO, before the consulate decides whether to approve a US visa application.

As part of that process, US Immigration and Customs Enforcement agents stationed in the embassies can be tasked to carry out detailed checks in the applicant's home country.

A deeper investigation was not, however, requested for Malik because routine background checks turned up no "derogatory information" that raised the suspicions of visa reviewers, the official said.

It was the latest twist in the case of US-born Syed Rizwan Farook, 28, his Pakistani-born wife, Malik, 29, who investigators said became radicalised long before they killed 14 people in a shooting rampage in San Bernardino, California, on Dec 2.

Questions have been raised whether the US government missed any warning signs of the attack, which investigators believe was inspired by, but not directed by, the militant Islamic State (IS) group.

Visa process scrutinised

How Malik was secured her spousal visa, known as a K-1 visa, has come under close scrutiny.

In carrying out checks under an SAO, ICE agents "may conduct applicant interviews, additional database checks, a physical document review and liaison with local law enforcement officials", said a 2009 Department of Homeland Security (DHS) paper that described the investigation procedure.

In Malik's case, though, since earlier background checks did not raise suspicions, no SAO or field investigation was requested before she was granted a visa to enter the US as Farook's fiance, the official said.

A spokeswoman for the Department of Homeland Security, which oversees ICE, declined to comment.

Routine visa background inquiries usually include checking a visa applicant's name against various spy agency and law enforcement databases, but would not normally involve extensive investigations in the applicant's country of origin.

Absent a compelling reason for consular officials to ask for an SAO investigation on a visa applicant, officials said, such checks normally would not be conducted.

In 2014, the US government issued over 10 million visas, according to State Department data.

It is unclear, however, whether even an SAO investigation of Malik would have turned up information that might have raised questions about whether Malik should have been awarded a US visa.

Officials have said that before being granted a visa, Malik underwent national security and criminal background checks conducted by Homeland Security, the State Department and US spy agencies.

She was also interviewed by the US consulate in Pakistan, and the New York Times reported that she was interviewed by a US immigration officer in America before being granted a permanent resident's green card.

US officials have said that Malik and Farook were completely unknown to US spy agencies before the San Bernardino shootings.

Social media

US officials have also acknowledged that under visa vetting procedures at the time that Malik applied for her visa, no one routinely checked applicants' social media postings for irregularities.

Officials familiar with the investigation into the shootings say that it was discovered after the shootings that Malik began posting social media messages demonstrating a sympathy for militancy before her US visa was granted.

At the time, US officials involved in vetting visa applicants were under pressure from the Obama administration to avoid looking at visa applicants' social media postings out of respect for their privacy and civil liberties, two former DHS officials said.

Other officials familiar with post-shooting investigations into Malik's background said that Malik posted her pro-militancy messages under a pseudonym and also activated privacy settings, which meant that any alarming messages would have been difficult to find even if visa reviewers had been able to look for them.

Two US officials said on Tuesday that even the message Malik posted around the time of the shooting in which she pledged allegiance to IS would have been hard for investigators to discover because she posted it on someone else's Facebook page.

Shooters buried in quiet funeral

Syed Rizwan Farook and Tashfeen Malik were buried Tuesday in a quiet, graveside funeral guarded by FBI agents.

Many of those who attended mosque with the couple refused to attend, two mosque members said.

The funeral followed traditional Islamic rituals, said an attendee. At a Muslim cemetery hours away from San Bernardino, the bodies were cleansed according to Islamic rules, wrapped in white cloth and buried.

The funeral attendee and another person familiar with the situation, both of whom asked not to be identified for fear of retaliation, said it took a week to find a graveyard willing to accept the bodies.

They said the husband and wife were ultimately buried in a cemetery far from San Bernardino, after a closer facility refused to take the bodies because of fears the graves would be desecrated. Neither person would identify the cemetery where the couple was buried.

Muslims are usually buried within 24 hours of dying, but family members and community members had to wait for the bodies to be released by law enforcement officials and then for permission from a cemetery.

Neither source would say which cemetery refused to bury the couple, but a woman at the Islamic Cemetery & Masjid in Adelanto, Calif. ─ less than an hour from San Bernardino ─ confirmed the cemetery had refused to bury the bodies, in part out of a fear of backlash, but also for "other reasons". She declined to give her name.

The family of Tamerlan Tsarnaev, one of the two men accused of carrying out the Boston Marathon bombing attack in 2013, faced similar difficulty finding a place to bury his body after the attack.

Graveyards in Massachusetts refused to accept the body, and the family ultimately buried him in an unmarked grave in Virginia.

About 10 people went to the funeral, the attendee said, including members of Farook's family and people who used to pray with him at mosques in San Bernardino County.

But most Muslims in the community refused to participate in the burial or perform Salat Al-Janazah, according to the source who did not attend the funeral.

"I don't forgive him myself," said the mosque-goer who did not attend the funeral. Still, he added, "I pray mercy for him, and we Muslims know God is merciful. But he's also just."

Farook and Malik left behind a 6-month-old daughter, who has been in state custody since the Dec 2 massacre. Farook's sister and brother-in-law, Saira and Farhan Khan, have said they hope to adopt their niece.

An attorney for family members did not immediately return a call seeking comment for this story.