The path of killers

4 murders, every other day, in 4 different towns, all strangled, are finally linked together. The task force in charge of finding the serial killer or killers quickly find some clues. Still not having any idea who the killer is, they come up with the idea that he is not killing people he knows but strangers with no desire to steal or do anything to them. They are forced to find a pattern in the killings and anticipate the next one to catch the killer. A fifth killing on the 9th day brings more clues and the sixth killing on the 11th day confirms their pattern. They prepare to catch the killer on the 13th day, and someone shows up, exactly where they expected him to. They tell him to freeze but he ignores them and attempts to strange his target. He is shot multiple times but somehow escapes. Most of the police think he will change his pattern after being caught, or go back to finish the job of the last one, but a few follow it anyway to the next potential target. The killer arrives again and again is shot while escaping. But this time they get proof (I don't know how yet) that the killer is not human. Eventually they find out he is an alien and he has lost communication with the rest of his species. They realize that every murder is broadcast over satellite and that the name of the victim, the date and city the victim is from is all part of a message set back to his people. He is killing to communicate. Eventually the police break the code. He is transmitting whether or not the earth is a good planet to gather resources from, and if it is, the aliens would attack. When the police finally figure out how to catch the killer and accomplish it, they realize that the pattern points to communicating that the aliens should come. The police realize that they have to kill 4 more people in 4 different cities to continue the communication and let the aliens pass our planet by.