PORT HURON, Mich. -- The Port Huron Police Department discovered threatening letters to the city government while conducting a search at a resident's home Wednesday.

Police were called to the home on the 800 block of Howard Street after neighbors reported disorderly and threatening activities.

During the search, police found letters and papers containing threatening messages to the local government.

Several of the threatening letters were identical to the letters that had been found in various locations around Port Huron in the past few years.

Police said electronic equipment and materials that were used to make the threatening letters were also confiscated.

A 41-year-old woman and her 17-year-old son, who both live in the home, were arrested on unrelated charges.

The investigation into the threatening letters continues.