San Bernardino killers Isis Islam
San Bernardino killers Tashfeen Malik, (L), and Syed Farook passing through Chicago's O'Hare International Airport in 2014REUTERS/US Customs nd Border Protection

The US Federal Bureau of Investigations (FBI) says San Bernardino killers Tashfeen Malik and husband Syed Farook did not post public comments in which they expressed support for martyrdom. FBI director James Comey says they made the comments in private direct messages on a social media outlet. The outlet wasn't named but the Washington Post quoted officials saying they were on Facebook, where Malik did post a message pledging allegiance to the Islamic State (Isis) prior to carrying out the attack, in which 14 people were killed.

The report comes as US security officials come under pressure to explain how Malik and Farook managed to slip through the net. New York Senator Chuck Schumer said: "Had they checked out Tashfeen Malik, maybe those people in San Bernardino would be alive".

If the latest reports are accurate and the couple's pro-Isis comments were made in private messages, questions could arise about whether it is technically feasible or politically and legally acceptable to monitor direct messages as well as emails and text messages. US Republican candidate Donald Trump, who used the killings to make inflammatory remarks about Muslims, has said he would consider shutting down parts of the internet to keep America safe.

Chattanooga suspected gunman
Mohammad Youssuf Abdulazeez was influenced by foreign Jihadists when he shot 5 people dead in ChattanoogaHamilton County Sheriff handout

In a digital age, Comey singled out Twitter as a tool used by Jihadists to spread their messages of hate. "Twitter works as a way to sell books, as a way to promote movies, and it works as a way to crowdsource terrorism - to sell murder," Comey told a counterterrorism conference in New York City.

Comey also said Chattanooga killer Muhammed Youssef Abduladeez was inspired by a foreign terror group. It's the first time the FBI has made the claim about the motivation for the killings, in which Abduladeez shot dead four Marines and a navy soldier before being killed by police on 16 July. In the same conference, Comey said that Abduladeez was "inspired by terrorist organisation propaganda."

US President Barack Obama will meet relatives of the San Bernardino shootings when he visits the California town on Friday (18 December). In a statement the White House said: "Obama's visit to Southern California was added to his previously scheduled trip to Hawaii, where he and the first family will celebrate Christmas, as has been their tradition during his presidency."