A man charged with sending hundreds of hoax letters containing a mysterious white powder was arrested in Texas by US law enforcement on Monday.
Hong Ming Truong, 66, was charged July 25 in federal court in the Northern District of Texas for sending what "may have reasonably been believed" to be anthrax since 2008, according to the complaint.
In each case, the powder was found to be harmless, but caused panic and strained the resources of law enforcement.
More than 500 of such letters were sent to Lockheed Martin in Grand Prairie, Texas and schools across the country. In June 2013, HAZMAT teams responded to the letters in 28 public schools in Boston.
Letters containing the white powder sent in May 2012 began with "Al Qaeda back!" and aligned the writer with the militant Islamist organization.
The FBI and the US Postal Service investigated Truong. The agencies said that the language of the letters, all originating from Northern Texas, indicates that they were all sent from one person.
Truong will remain in custody as the case proceeds.