Now officials are offering a reward of up to $150,000 for information leading to a suspect's arrest, prosecution, and conviction.
Officials say they think one individual has, since 2008, sent more than 380 letters to elementary, middle and high schools; day care centers; churches; government offices; US Embassies abroad; restaurants; and other private businesses. Each letter was sent through the US mail and featured a postmark from North Texas.
During the week of May 7 alone, more than 20 letters containing white powder were received by early childhood development centers, elementary schools, and an aerospace-related business across Texas and several other states, according the FBI. FBI officials in Houston say the suspicious letters sent to Houston ISD schools last week are among those 20 letters.
So far, investigators believe a total of 22 suspicious letters sent to Houston-area facilities since 2010 were mailed by the same individual.
None of the mailings to date have contained hazardous materials.
Detectives say the author has and continues to reference subjects such as al Qaeda and the Nazi SS, which is believed to have been included for shock value rather than to express any sincere sympathy or affiliation. In a recent letter, he used the terms "Scooby Doo" and "triple dealer spy" and made reference to CIA counterintelligence and FBI internal affairs.
No other details were immediately available.
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