A total of five people are in custody on suspicion of child abduction, South Yorkshire Police said, after teenager Erika Kacicova, who had been missing for six days, was found.
The police said they were four men and a women.
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Police believe it is a "distinct possibility" that Halliwell was a serial killer, beyond the two murders he was convicted for.
The bodies were seen lined up in white and black body bags along Libya's western shoreline in stark and grim images released by aid workers.
Rebecca Steinfeld, 35, and Charles Keidan, 40, objected to the "patriarchal baggage" of "the institution of marriage".