It’s over 20 years since I read that book.Deirdre Jacob was picked up by a stranger apparently.
If I recall correctly it covered 6 cases, 5 of which had definite key suspects, just insufficient evidence. In my head Jo Jo was the 6th girl who just vanished but I could be wrong. We know now who was responsible for her murder.
I understood the poor Deirdre Jacob girl was the only one of the 6 who could be linked to Larry Murphy. Deirdre had visited her grandmothers in town that day and disappeared on the walk home. It was later discovered that Larry Murphy a carpenter was working on her grandmothers roof around the time. An invoice/receipt was discovered in the grandmothers papers.