Private Detective novel with some sci-fi elements. Came out late 80's, early 90's?

I don't really remember much about this. The main character was a private detective. He had a gun with a 4 dimensional clip, that held 100,000 rounds.

At one point during the story, he has to enter a secret, government, underground laboratory and retrieve an alien artifact. When he reaches the bottom level, he finds all the personnel are dead. Their bodies are withered and leathery-looking.

He finds the artifact and is leaving, when one of the corpses exhales a cloud of green, glittering gas. The other corpses begin to do the same. He panics and runs for the elevator. The gas follows him. As the elevator is returning to the surface, the gas begins to seep through the door. In desperation, he grabs the fire extinguisher and sprays the gas with it. The gas retreats and he escapes.

That's all I remember. Does it ring any bells for anyone?