This book is sloppy - read on KU
The spoilers are minor and do not tell you who committed the crime or why.
I'm not sure how this series is so highly rated. It does have some positives. The pacing is decent. The story line is fine, although you know who it is for a long time, but you don't know the why of it until the end. There are two minor twists. One was extremely obvious.
For starters, I think special agents in the FBI are probably pretty picky about that "special" part of their title. The book is inconsistent with including that word. I understand it would be cumbersome to always use it, but there are multiple times when Jo is introduced without it. And there is a significant difference between special agents and plain agents. I've never read an FBI series where it wasn't made clear the agent was a special agent.
I think it's their second day on the case when Ford picks up Jo at 8 am and they go to talk to one witness in town. Afterward, he drops her off, she updates her boss on the interview, and leaves for the day. Somehow the 30 minute at most interview and updating the SAC took her from 8 am to evening again. I reread it to make sure I didn't miss anything.
The teenager killed is repeatedly stated to be 16, even by the ME. Her gravestone lists her life from December 29, 2006 to April 3, 2022. That would make her 15. In addition, and this is a small thing, gravestones, in my experience, take weeks or months to be engraved and installed. Maybe you jump to the front of the line if you're rich when you die.
The guy the teen had been dating went to public school and that's one reason her parents disapproved of him. They make a big deal of how he kept showing up at the private school the girl attended and that security had to force him to leave. (These weren't stalking incidents. He was showing up to take her to lunch, etc.) Late in the book, the sad teen reminiscences about meeting her in world history class. Not sure how that happened from different schools.
When they try to call the person they know to be the murderer, someone else answers the phone at the residence who is unrelated. It is written as the phone belonged to the residence and not the individual, which has never been the case unless it is a dorm or some place that would provide a phone line, which is highly unlikely. Even with landlines, numbers followed the individual when possible or were shut off when not.
The first minor twist that most will see coming is based on some math that Jo does. The math doesn't add up, other than it being in the very bague ballpark. I apologize for being cryptic, but that's to keep it from being much of a spoiler.
The last blunder I noticed was the teen who didn't kill the family, which is obvious from the blurb, joins the military just a couple of weeks after the case ends and is leaving for basic the next day. There are multiple issues with this. One, the military won't take someone who hasn't graduated from high school. At one point, they wouldn't take someone with a GED without a high ASVAB score, the latter of which he could have had, but he didn't have the former. For those the military does take, it's usually months before they're shipped off. I've seen a lot of friends' teens join recently, and it's never 2 weeks after they sign up.
I won't even bother with what seemed questionable on police procedure, and I'm sure a police detective or a special agent with the FBI would have a laundry list of errors, but that's probably true with most crime thrillers.
There were some minor grammatical errors. I'm wondering where the author has lived that he refers to headlights on cars as headlamps.
Some of these issues I could see with an author's first book, but this wasn't. While it is most important for the story to be engaging, and it mostly was, a good editor should have caught most of this. It certainly isn't professional quality.
I read the reviews complaining about the number of times "smirk" was used. I used the search feature, and it came up 7 or 8 times each in book 1 and book 2.
I'm going to try book 2 to see if it is an improvement.