It was like 12 years ago when I read this book. It's considered a juvenile fiction, but it was worth the read. It's called Zachs lie. This is a copy paste from a quick review about it.
When Jack Osborne is befriended by his school's custodian and a Basque girl, he begins to adjust to his family's sudden move to Elko, Nevada, after entering the Witness Security Program, but the drug cartel against which his father will testify is determined to track them down.