The substance found with a letter at the St. Louis County Courthouse in Virginia on Friday has been tested and found not harmful, the St. Louis County Sheriff's Office said.

The court administrator's office where the letter was opened was evacuated on Friday afternoon as a precaution but will reopen as normal on Monday, the sheriff's office said in a news release on Saturday.

Tests done on Friday evening determined there was "no health or safety risk to those exposed during and after the letter had been opened," the sheriff's office said.

The letter was taken to the Minnesota Department of Health for testing.

The sheriff's office is continuing to investigate to determine who was responsible for sending the letter.