Which method is illegal for gathering information on a subject?

Pre-texting is considered illegal when it involves obtaining information under false pretenses or misleading circumstances, particularly when it violates privacy laws. This practice often involves impersonating someone else or using deceptive tactics to extract personal information from a third party.

In contrast, surveillance is a legal method utilized to observe a subject's activities, as long as it is conducted in public places where there is no reasonable expectation of privacy. Interviewing witnesses is also a standard investigative practice, as long as it is done ethically and lawfully. Additionally, legal database searches involve accessing publicly available records or databases, which is permissible under the law.

Thus, pre-texting stands out as illegal due to its deceptive nature and potential infringement on individuals' rights and privacy, making it distinctly different from other methods listed.