In the late 1970s , the relationship between the two became tense , and Sapir withdrew .
The series was initially co-authored by Warren Murphy and Richard Sapir , with each writing a portion of each book separately .
In the late 1970s , the relationship between the two became tense , and Richard Sapir withdrew .
The series was initially co-authored by Warren Murphy and Richard Sapir , with each writing a portion of each book separately .