Federal probe of letters containing suspicious substances widens as GOP senators report receiving mailings

A federal investigation of letters containing unknown substances that were mailed to elected officials’ offices has expanded as some Republicans have been identified as targets of the mailings, a person with direct knowledge of the investigation told NBC News on Friday.

A federal investigation of letters containing unknown substances that were mailed to elected officials’ offices has expanded as some Republicans have been identified as targets of the mailings, a person with direct knowledge of the investigation told NBC News on Friday.