The author is a retired chemistry professor who wrote many textbooks on chemistry. He had been interested in the Borden Murders for decades. After he retired, he began his research by reading the microfilmed Fall River newspapers from that time, and other sources. His book is his solution to the mystery; but you can "come to your own conclusions".
The index has an entry for "Simpson trial", but not one for "Eagan, Ellan". His sources do not list Edmund Pearson's 1935 book (which is not generally available); it was the first book to renew interest in this unsolved crime. The book contains some reproductions from those newspapers, but some of the photographs are of low quality. He imagined a "simple logical explanation" for the missing note to Abby. In Chapter 14 he created a new theory: Andrew was killed first, then Abby! This goes against all known facts of the case, and the testimony of those who were present. He did not explain the purpose of his theory; could it have been caused by a more recent event where the time of death could be calculated by the fresh red liquid blood of the victims? The author attempted a solution to the mystery; I think he should have done more research.
Arnold R. Brown's book is still the best solution; he did more research, and had the hometown advantage. A number of minor spelling mistakes suggest that this book was rushed to publication.