in 2009, the federal bureau of investigation (fbi) released the results of a five-year-long study (the highway serial killings initiative) investigating the unsolved murders of prostitutes, hitchhikers, and stranded motorists. over 500 female victims have been compiled in a database, most of whom were killed or discarded at truck stops, hotels, and roadsides. the fbi has speculated that many of these victims were murdered by long-haul truck drivers, some of whom may be serial killers. investigators speculate that the easy access to potential victims, mobility, and lack of supervision enjoyed by long-haul truck drivers have contributed to this phenomenon. the head of the initiative, michael harrigan, says most of the victims lead high-risk lifestyles (e.g., prostitution) which left them particularly vulnerable. in 2004, the fbi began investigating a string of murders in which the victims were found along the interstate 40 corridor in oklahoma and several other states, which sparked the creation of the highway serial killings initiative.