As airport security is strengthened in Europe, a search of the last known London residence of the man who has been charged with trying to blow up a trans-Atlantic jetliner has been launched. 

As the criminal investigation got underway, there were many more questions than answers regarding the attempt to bring down an Amsterdam to Detroit airliner on Christmas Day.

One key facet will be to determine if the man charged with the attack, Umar Farouk Abdulmutallab, acted alone or in concert with others.

Terrorism expert Dr. Sajjan Gohel is from the London-based think tank, the Asia-Pacific Foundation.  He says finding that out will be crucial.

"Whether this was an act of terrorism conducted by al-Qaida central or that of a lone wolf acting independently, we will have to wait and see for the investigation and what comes out of that, but we do know that al-Qaida and their affiliates have a crazed obsession in targeting the aviation industry," said Dr. Gohel.

On Sunday, U.S. Homeland Security Secretary Janet Napolitano said at this stage there is nothing to indicate the 23-year-old Nigerian was part of a larger plot, but much more questioning will follow.

One effect of the attempt to blow up flight 253 is increased security at international airports in Europe.

Something Sajjan Gohel says passengers will just have to get used to.

"There is going to be disruption," he said.  There is going to be delays.  There is going to be greater scrutiny and in security and unfortunately we are just going to have to accept this, that this has become an inevitable part of our lives now whenever we travel abroad, especially for trans-Atlantic flights."

Graham Simpson is the operations director at Britain's busiest hub, Heathrow Airport.

"We are incurring some delays like all other airports are around Europe," he said.  "But we are working very hard with the airlines to minimize those delays.  Currently delays are averaging around one-hour and that is for flights that are going out to the U.S."

Passengers are being encouraged to check ahead with their airlines, to arrive an hour earlier than normal and to bring only a single carry-on bag with them.

Meanwhile in London, the multi-million-dollar apartment where Abdulmutallab lived during his days as mechanical engineering student at University College between 2005 and 2008 continues to be searched by police forensic teams.  Computers and hard drives in particular are being scrutinized in fine detail.

It is part of a larger investigation aimed at trying to identify those individuals he was in contact with.