The Sacramento Sheriff's Department is investigating a violent assault of a female employee at a Subway restaurant in Sacramento County.

About 6:30 this morning, a female employee in her early- to mid-20s was opening the doors at the Subway restaurant on Auburn Boulevard and Palm Avenue when she was attacked by a man in dark clothing and a mask. There is no other suspect description available at this time. 

Spokeswoman Lisa Bowman says a blunt object was used to beat her. She was then tied up and possibly sexually assaulted. 

The suspect then left the victim to free herself. She was finally able to call authorities about two hours later.

Investigators say they will examine all possibilities, including whether this suspect may be connected to a serial rapist involved in three other cases in the Madison/I-80 area. 

The victim was taken to an area hospital for treatment. 

The suspect is still at large and it is unknown at this time if the suspect took anything from the store.