SOLVED. Secret agent - partly supernatural thriller. [s]

[Buzz]

The story opens in Venice with a especially gruesome murder of an agent. The agent sent to investigate is visited often by the wisecracking ghost of the murdered man. The killer uses psychoactive gas to cause hallucinations. Later, an entire family in London is murdered. The climax of the chase takes place in the Southwest. The killer turns out to be Native American out for revenge. He had been using peyote dust. (Book was followed by a sequel)

[Buzz]

OK found it myself. Google is your friend.

My search string: Cia agent Venice murder London murder desert native american hullcinogen

"The Echelon Vendetta" by David Stone

Found it on Amazon, also here:

http://www.goodreads.com/book/show/28...

I loved it. I recommend it.