Why did 13 women willingly open their doors to the Boston Strangler?

The Boston Strangler (1968)

Directed by Richard Fleischer

Boston is being terrorized by a series of seemingly random murders of women. Based on the true story, the film follows the investigators path through several leads before introducing the Strangler as a character. It is seen almost exclusively from the point of view of the investigators who have very few clues to build a case upon.