John Worboys, 53, who may have committed more rapes than anyone else in British history, is serving an indeterminate sentence of at least eight years for using a date-rape drug to rape 12 young female passengers. The Crown Prosecution Service has said another trial is "not in the public interest," The Sun reported.
A police spokesman said the true number of victims is unknowable. Worboys, arrested in 2007, is believed to have attacked 30 women while on bail.
"The difficulty is that a large number of the women do not know whether they were raped or not," the spokesman said. "The only person who knows is Worboys himself. We hope he might consider telling us in the future what went on."
Women who say Worboys attacked them have received letters telling them he will not be prosecuted again.
Investigators said he offered the victims champagne, saying he had just won a lottery jackpot. Police said 102 women have come forward, 19 of them since the trial.
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