Speaking on BBC Radio Tuesday morning, British Home Secretary Alan Johnson confirmed that Abdulmutallab had been placed on a U.K. watch list after he was refused a student visa 14 months ago. He explained that people on a watch list cannot come into the UK, although they can pass through the country in transit.
Johnson said that he did not believe Abdulmutallab had been acting alone, and that police and security services in Britain are examining whether he was radicalised while in London. They are looking at "what happened when he was in this country, was he radicalised in this country, was there any association with whoever may have been behind this plot. We don't know yet whether it was a single-handed plot or (there were) other people behind it - I suspect it's the latter rather than the former."
Abdulmutallab was arraigned on terrorism charges in federal court in Michigan on Saturday. His next expected court appearance is January 8.
Jean Fievet contributed to this report from London, Dana Hughes contributed from Nairobi.