IMO, isolated case means not the work of someone who will strike again. In other words, the public is not in danger:
Investigators are still trying to track down the person who stripped Alanna naked, bound her hands and feet,
put a plastic bag over her head and ditched her beneath a tarp in the street.
Alanna's body was found wrapped in a tarp a mile and a half from her home in Saginaw, Texas, on Monday night. She her hands and feet were bound,
she had a plastic bag over her head and she was naked except for a pair of purple underwear.
Witnesses who discovered Alanna’s body have said she was bound and that her body was wrapped in a tarp with a belt.
Her head was also covered with a bag, they said. http://www.dallasnews.com/news/crime/headlines/20130708-in-saginaw-more-questions-but-no-answers-in-girls-slaying.ece