The Muslim Community was suspicious of them
according to this article:
NEIGHBORS SUSPICIOUS
Khalid Qazi, president of the American Muslim Council of Western New York, said he was told that the investigation started when some in the local Muslim community reported suspicious activities to the FBI.
In his announcement Saturday, Thompson said that while “we do not want to get into the details of the investigation ... we have had great cooperation from the Muslim-American community, and we appreciate that a great deal.”
I appreciate it, too. Bravo!