After the Serial Killer Ted Bundy Was Captured, He Participated

After the serial killer Ted Bundy was captured, he participated in a number of interviews and took various psychological tests. The interviews with him were particularly valuable to researchers, because his level of sociopathy is rare, and perpetrators are often unwilling to assist researchers. Therefore, his case was ideal for a/an

A) case study.
B) naturalistic observation.
C) operationalization.
D) correlational study.