Kids' mystery with dog

My daughter's 31 year old friend fondly remembers a children’s mystery series about a boy and his dog solving mysteries. We think that there’s a character named Liam.

Published pre-2000 or very early 2000s

Long shot, but if we allow for two girls and a dog, there are the Something Queer books by Elizabeth Levy.

Try browsing Dogs -- children's/young adult fiction
https://www.librarything.com/list/1026/Dogs-childrens%25252Fyoung-adult-fiction

Possibly the Bloodhounds, Inc series by Bill Myers. I don't remember a Liam in the series, but not sure about that.

Jack Russel series, maybe?