• Metrojet disaster has put new focus on airport security around the world
• Peter Bergen: Airports are vulnerable to militants who can get access through their jobs

Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of "Manhunt: The Ten-Year Search for bin Laden -- From 9/11 to Abbottabad."

(CNN)Concern that there might have been a bomb smuggled aboard the Metrojet flight by an insider at Sharm el-Sheikh airport raises the question: Could such an insider attack happen in the West?

U.S. and UK officials have said there is reason to believe a bomb brought down the Metrojet flight, but Egyptian authorities say they have not zeroed in on a cause yet and there are other possible explanations. The five American terrorists who have worked at major American airports were recruited by variously ISIS; the al Qaeda-affiliated Somali terrorist group, al-Shabaab; a virulent "homegrown" jihadist cell based in California; and another such group in New York City. In the years after 9/11, Kevin Lamar James was jailed in California's Folsom prison where he formed a group that he conceived of as "al Qaeda in America." James recruited others to help him with his plans. One of them was 21-year-old Gregory Vernon Patterson who had recently worked at a duty-free shop at Los Angeles International Airport (LAX). James thought that Patterson's inside knowledge of LAX would be helpful for his plans and when he made a list of potential targets in California, James listed LAX. James' crew planned to attack around the fourth anniversary of 9/11. They financed their activities by sticking up gas stations and their plans only came to light during the course of a routine investigation of a gas station robbery by police in Torrance, California, who found documents that laid out the group's plans for jihadist mayhem. Members of the California cell are now serving long prison terms. At the time, senior FBI official John Miller said, "Of all of the terrorist plots since 9/11, it is probably the one that operationally was closest to actually occurring." Two years after the California cell were arrested, a similar group in New York City that had no links to any overseas militant organization plotted to blow up the underground pipelines that deliver jet fuel to JFK Airport. The leader of the group was Russell Defreitas, who had worked as a baggage handler at JFK and his insider knowledge helped drive the plot. He bragged to an informant that attacking JFK would have tremendous impact; "This can destroy the American economy for some time." Defreitas was arrested and he is serving a life term. On October 29, 2008, Shirwa Ahmed became one of the first Americans ever to conduct a suicide attack anywhere in the world when he was recruited by al-Shabaab to drive a truck loaded with explosives into a government building in Somalia, blowing himself up and killing 20 other people. Ahmed graduated from high school in Minneapolis in 2003 and then worked at the Minneapolis airport pushing passengers in wheelchairs; it was during this period that he became increasingly religious and was recruited by al-Shabaab. Abdisalan Hussein Ali became a suicide bomber for al-Shabaab in Somalia in 2011 and had also worked at the Minneapolis airport, in a Caribou coffee shop. Similarly, Abdirahmaan Muhumed, who was killed in 2014 while fighting for ISIS in Syria, had workedat the Minneapolis airport, where he had a security clearance that gave him access to the tarmac and to planes. In the United Kingdom, British Airways IT expert Rajib Karim, 31, conspired with al Qaeda's affiliate in Yemen to place a bomb on a U.S.-bound plane. In 2010, one of the leaders of al Qaeda's Yemeni affiliate, Anwar al-Awlaki. wrote an email to Karim asking, "Is it possible to get a package or a person with a package on board a flight heading to the US?" Karim replied: "I do not know much about US I can work with the bros to find out the possibilities of shipping a package to a US-bound plane." Karim had applied for cabin-crew training before he was arrested and was sentenced to 30 years in 2011. In 2006, an employee at a shop in Heathrow working on the "airside" post-security section of the airport provided advice about the security conditions to self-proclaimed al Qaeda terrorist Sohail Qureshi, who was convicted of multiple terrorism charges. Department of Homeland Security Secretary Jeh Johnson announced in June that he was implementing new measures to "address the potential insider threat" by mandating biannual background checks for workers at U.S. airports, while also requiring airports to reduce the number of access points to secured areas and to increase randomized screening of airport employees. These are welcome developments. On Friday, Johnson announced additional screening procedures for flights coming to the U.S. from a variety of airports in the Middle East. What precisely those new security procedures consist of is not being advertised and while the new measures for U.S.-bound flights from the Middle East may serve to allay some travelers' worries, the question is whether they address the fundamental issue, which is how good are the vetting procedures for airport workers at the points of origin for Western-bound flights? At Sharm el-Sheik airport, the answer to that question may have already presented itself.