A lot of potential, but the presentation leaves a lot to be desired.
The writing quality is only so-so, at times verging into hyperbolic, blog-type, don't-trust-your-readers-to-be-able-to-know-horrible-monsters-without-you-telling talk.
Also, the book is riddled with very basic factual errors; as just one example, serial killer Roy Norris is consistently referred to as Ray Norris.
In many entries, the details of the crimes are scant, sometimes to the extent that victims are not even identified. This is not due to lack of available info; I was able to find such information readily with good old Google. Surely the author, who is no novice crime-writer, could have done the same?
I did like that in a few cases, the author pointed out (with supporting evidence) that the death sentence was possibly ill-advised or disproportionate, and in the final entry, Tommy Zeigler, he is emphatic (and to my mind, justifiably so) that the man on Florida's death row is the wrong one. And he even includes contact info if anyone has a tip to solve that case of multiple murder and attempted murder.
I really like the A-to-Z format as well, and this is true about books on almost any subject. I fell in love with encyclopedias at a very early age.
The cases span several states, most notably Texas, Arizona and Kentucky. The time range is generally from the 1990s on, though there are some 1980s cases, and one oddball from the 1930s. Here is another area where some help from a seasoned editor could have helped to either broaden or narrow the scope of the entries.
In summary, good for a start, but my Lord, don't use this as a primary source for your next term paper, because if so you'll look like a clown.