PONTIAC, Mich. (AP) — Police believe one man could be responsible for a series of armed robberies throughout the Detroit area.

The Oakland County sheriff's office says at least eight businesses have been held up at gunpoint over the past three weeks.

The suspect covered his face with a mask or scarf in a robbery this weekend at a sandwich shop and an attempted robbery of a flower shop. Both were in Pontiac, northwest of Detroit.

The Pontiac cases are among seven in Oakland County. The sheriff's office says two holdups were committed in Auburn Hills and three more in Waterford Township.

Robberies also are being investigated in St. Clair County's Port Huron and Hartland Township in Livingston County.