MOGADISHU, Somalia -- As Americans finalize their holiday travel plans, terrorists overseas are busy constructing sophisticated laptop bombs that can be smuggled onto planes. An attack took place in Somalia in February of last year.

CCTV footage shows two men going into the airport from the tarmac. One is carrying a laptop. At one point, he slips the rigged computer to the bomber in the coffee shop.

The man was the head of Mogadishu's airport security at the time.

The laptop exploded shortly after takeoff, and blew a hole in the side of the plane. Passengers remained calm. Only the bomber was killed.

But Islamic militants of al-Shabab continue to try and perfect the laptop bomb. In fact, they'd tried to plant a bomb a day earlier, but the flight was canceled.

In the past 18 months, three other computer bombs were found after one partially exploded in a cargo hold.

New multi-layered security checks, including dogs trained to sniff out explosives, are supposed to stop that. But al-Shabab still has people on the inside.

"So, the biggest problem we have is that no matter who it is, from the airport manager to the cleaner, everybody has to follow the security," said Said Eliye, deputy head of security.

The militants operate freely in the crumbling city of Mogadishu. CBS News has been repeatedly told that al-Shabab has eyes and ears everywhere. Their members blend easily into local communities. A seemingly quiet road may not look very menacing, but it can turn nasty in an instant.

A truck bomb in October killed 500 people and injured hundreds more. According to intelligence sources, the bomb went off early. It was meant to hit the airport, which is located nextdoor to the U.S. embassy.

A senior intelligence source told CBS News al-Shabab now appears to have international support. The bomber's ticket from last year's laptop bomb was bought in Angola. The flight was bound for India, where the bomber had a Visa and pre-paid medical treatment.

Somali intelligence say they believe the laptop bombs are the work of the same bomb maker who was possibly trained outside of the country. They say the explosive devices all carry his trademark signature: the use of a 9-volt battery.