Mom's boyfriend accused of molesting sisters

After 12-year-old came froward, older sister also claimed she was assaulted

St. Johns County Sheriff's Office booking photo of Robert Skipper

ST. AUGUSTINE, Fla. – St. Augustine police say a 39-year-old man arrested Friday on a charge of capital sexual battery involving a 12-year-old girl was charged Tuesday on accusations he also assaulted the victim's 20-year-old sister.

According to St. Augustine police, Robert Lee Skipper's girlfriend reported that he had intercourse with her stepdaughter and forced her to perform oral sex on him over a six to seven month period. She said she had been afraid to tell anyone because Skipper had threatened to kill her.

Police searched the home and seized several clothing items and bed sheets as evidence.

Once the younger sister -- now 12 -- came forward, police said they learned her 20-year-old sister was also a victim of sexual assault by Skipper.

Skipper was booked into the St. Johns County jail on one count of sexual battery.  A second count in connection with the assult of the older sister was added Tuesday afternoon.