Feds offer $150,000 reward in probe of hundreds of letters with white powder May 17, 2012 -- Updated 0021 GMT (0821 HKT) An estimated 380 white-powder envelopes have been mailed since 2008 All the envelopes proved to be harmless with no toxic substances The FBI and Postal Service are focusing on the Dallas-Fort Worth area (CNN) -- Federal agents have been stymied in their long and fruitless search for a man who mails envelopes containing white powder and usually a message of some kind. Investigators from the FBI and U.S. Postal Inspection Service in the Dallas-Fort Worth area in Texas hope that a reward announced Wednesday may help locate the individual who has now sent an estimated 380 white powder envelopes since he first began his annoying practice in 2008. Analysts have developed few clues to date, because the mailer has managed to erase fingerprints or other identifiers. They believe he is a male, 30 years of age or older, who may be considered by others to be odd or eccentric. He may have some experience with mental health facilities, according to a reward poster prepared by authorities. The FBI in Dallas and Washington would not comment on whether the individual is the same one who early this year sent white-powder envelopes to dozens of members of Congress. However, the FBI in Dallas says the man seems to have recently focused more on schools than government offices. All of the envelopes proved to be harmless, and contained no toxic substances. However, in the past two weeks the man has sent more than 20 white-powder letters to early childhood development centers and elementary schools. Officials stress every envelope has to be carefully screened. The process is time-consuming and expensive. The reward provided by the FBI in Dallas and Postal Inspection Service Office in Fort Worth totals $150,000 for information that leads to the arrest, prosecution and conviction of the perpetrator.