Terminal Secret - a mystery and thriller rolled into one by Mark Gilleo

Terminal Secret - a mystery and thriller rolled into one by Mark Gilleo
https://www.amazon.com/Terminal-Secret-Mark-Gilleo-ebook/dp/B074V8LGCC

Dan Lord is a private investigator with a law degree who isn't opposed to the occasional barroom brawl. DC Detective Earl Wallace is a 25 year veteran with a new female partner from the suburbs. When Dan is hired by the wife of a congressman and Detective Wallace investigates the body of an attorney shot on her doorstep, there is little to tie the two together.   But as the body count rises and the clues accumulate, both parties realize they could be searching for the same criminal responsible for a series of unsolved crimes.