How do narco tests get information from criminals?

Year 1995 Police arrested an American youth named Andres English-Howard on the charge of murdering his girlfriend. But Andres did not confess to the court or the police about the murder of his lover Andrea O'Donnell. Suspect Andres was questioned many times but repeatedly said only one thing, he had no recollection of anything.
Andres couldn't remember a lot of things at the time because of the cocaine. The police could not solve the murder in any other way. At the end, they resorted to narco test with the permission of the court. Andres could no longer hide the fact that he killed his lover under the influence of drugs. It is known that he killed his lover in anger. Andres later committed suicide in jail. Narco testing is done to find out the mystery of many such unsolved cases. It is also known as truth serum. This test is often seen in various series or movies. In reality, this test is conducted by the police or law enforcement officers to find out the details of the crime. In this test, a special drug is injected into the criminal's veins. The person administered the drug loses some consciousness, though not completely unconscious. In this situation, the criminal is asked one question after another. It becomes difficult to hold back the truth, despite reluctance, because one does not have complete control over oneself.

Even in ancient Rome, people tried to learn information by drinking alcohol. In modern times, truth serum was first used in a criminal case in 1903 in New York, USA. Although there is a lot of controversy, this method is used in several countries including the United States, India. According to the rules, a person's consent is required for a narco test. This test is conducted on criminals or suspects to solve important crimes and cases. Investigating agencies perform this test when the evidence in a crime case is weak or unclear. The drugs sodium pentothal, scopolamine and sodium amytal are used in this test. The dosage is determined based on the target person's gender, age, health and physical condition. A sleep-like state develops in the criminal after administration of the drug. The person becomes hypnotized during this time. It affects the nervous system. Some unconsciousness comes without complete loss of consciousness but consciousness remains active. The person taking the serum then no longer has control over themselves. So it becomes difficult to retain information.

In India, authorities used truth serum on Ajmal Kasab in the 2002 Gujarat riots case, Abdul Karim Telgi fake stamp paper scam, 2007 Nithari murder case, Mumbai terror attack. According to the judgment of the Supreme Court of India, narco analysis, brain mapping and polygraph tests cannot be conducted without the consent of a person. In response to a petition questioning the validity of such tests, such tests are illegal and a violation of individual liberty. Statements made during a narco analysis test are not admissible in court. In certain circumstances, the court allows this examination after understanding the facts and nature of the case.

The test was conducted in a government hospital after a court order. During the examination, the investigating officer first briefed the doctors. Then the psychologist and investigating officer held a meeting with the concerned person. Experts contact the suspect and inform him about the test. The consent of the person concerned is mandatory for this test. When the psychologists realize that the suspect has understood the test, the testing process begins. The investigating agency interrogated the concerned person in the presence of doctors. Everything is captured on video at this stage. After analyzing the interrogation data, the experts prepare the report. Officers of the Forensic Science Laboratory supervise the entire work.

Source: NDTV and Science and Society, McGill University, Canada