Another suspicious letter found at Seattle synagogue

SEATTLE - Seattle police are investigating another incident involving a suspicious letter that was found at a synagogue, making it the fourth incident since Friday

On Monday night, the Seattle Fire Department responded to the 6200 block of 43rd Avenue to investigate a possible hazardous substance. Crews later determined it wasn't hazardous. 

Last Friday night, police responded to report of a suspicious package at two locations. 

The first location was at the 6500 block of 52nd Avenue South and the second location was in the 5400 block of Wilson Avenue South. The incidents were about an hour and a half apart. 

When crews arrived at the first location, they found a white powdery substance in an envelope and later determined it was not hazardous. 

At the second location, a similar package was found and it was believed to be non-hazardous also. 

The Seattle Police Department's bomb secured the second suspicious package. 

As police were investigating at the two locations, a person called 911 to report a suspicious package in the 4700 block 17th Avenue Northeast. This package didn't have a white, powdery substance.  

FBI Seattle told FOX 13 investigators are working to determine how many letters, who is responsible and the motive behind them. 

There have been no reports of injuries. 

The investigation remains ongoing.