Nirmala Devi, who was arrested on charges of attempting to traffic girl students, on Thursday appeared in Forensic Science Laboratory, Chennai, and gave voice samples. The suspended assistant professor was accused of asking students to extend sexual favours to some officials in return for marks and money. The suspect furnished voice samples over a telephone line to a recording device and tapes were also recorded, sources said. The samples would be compared with the audio tape that led to her arrest.