The substance, which has been sent to the state crime lab for analysis, was found in an envelope at the mosque just before 9 a.m. Friday. 

Police say a 43-year-old man was exposed to the powder, but was not injured. Police say experts at the scene determined there was no danger to the surrounding community. 

Authorities had everyone in the building shelter in place and the street outside the center was closed for three hours while authorities, including the FBI, state and local police investigated, AP reported. 

The Connecticut chapter of the Council on American-Islamic Relations says the envelope contained a white substance and a letter that included derogatory comments about Islam. 

The organization is calling for increased security at other Islamic institutions.