In a major blow to investigating agencies, the Supreme Court today declared as illegal, the use of narco-analysis, brain-mapping and polygraph tests on suspects. A bench headed by Chief Justice K G Balakrishnan said, no individual can be forced and subjected to such techniques involuntarily, and by doing so it amounts to unwarranted intrusion of personal liberty. It said, forcing an individual to such methods of investigation violates the scheme of legal process. <br/>Even if a person is subjected to such a mode of investigation on consent, the result of the test cannot be an admissible piece of evidence. However, the bench said, if anything obtained by the investigators from such techniques in which a person had volunteered, the agencies can use them for further probe. <br/>