Nothing Left (Jack Widow 16) by Scott Blade

Two murdered cops.
A lone policewoman.
One suspect--Jack Widow.
A cold night, in the middle-of-nowhere, in a vast county in New Mexico, a lone patrolwoman comes across a pair of dead cops sitting in their cruiser. And who does she find standing over their corpses? A giant, lone drifter with one stark trait; he is menacing like a nightmare. His name? Jack Widow.
To find the real killer, she'll have to partner with Widow. What seems like an ambush and execution might turn out to be something conspiratorial and far more sinister.