To prevent murder ...
There was more to watch for now. New information had crossed the invisible network that connected all watchbirds. New data, new ways of detecting the violence of murder.
There! The edge of a sensation! Two watchbirds dipped simultaneously. One had received the scent a fraction of a second before the other. He continued down while the other resumed monitoring.
Condition four, there are some living organisms who commit murder without the signs mentioned in condition three.
Through his new information, the watchbird knew by extrapolation that this organism was bent on murder, even though the characteristic chemical and electrical smells were absent.
The watchbird, all senses acute, closed in on the organism. He found what he wanted, and dived.
Roger Greco leaned against a building, his hands in his pockets. In his left hand was the cool butt of a .45. Greco waited patiently.
He wasn't thinking of anything in particular, just relaxing against a building, waiting for a man. Greco didn't know why the man was to be killed. He didn't care. Greco's lack of curiosity was part of his value. The other part was his skill.
One bullet, neatly placed in the head of a man he didn't know. It didn't excite him or sicken him. It was a job, just like anything else. You killed a man. So?
As Greco's victim stepped out of a building, Greco lifted the .45 out of his pocket. He released the safety and braced the gun with his right hand. He still wasn't thinking of anything as he took aim ...