A judge said the four accused could no longer contribute to the police investigation and served no purpose in custody, PTI reported. They have been ordered not to leave the country.
The victim told police she was part of a tour group visiting India in April last year when her local guide gave her a spiked bottle of water and raped her with acquaintances inside her hotel room.
Four men were later charged with her rape.
The woman returned to New Delhi in December to record her testimony in court and identify the suspects.
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She told investigators she had no memory of the assault for nearly three months after she returned from India.
"The first two nights I was drugged, physically assaulted and sexually assaulted," she told an Indian news network at the time.
"I had no memory of what happened to me while I was in India. I regained my memory three months later around the end of July and that's when I took action," she said.
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The tour guide, a driver, a cleaner and a hotel employee were arrested after police received her formal complaint through an American charity.
Early last year a German tourist accused two men of taking her captive and raping her in southern India. A 35-year-old Japanese tourist was also raped in India last December.
India faced international scrutiny over levels of violence against women following the fatal gang-rape of a medical student in New Delhi in December 2012.
India introduced tough laws against sex offenders in wake of the fatal gang-rape but high levels of sexual violence against women continues.
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