1.Predators by nature are designed to feed on smaller animals called prey for food. While a killer were not natural build for that, they developed it from bad association.
2.Predators is implied to animals while a killer is implied to a human
3.They hunt down animals not by contract but killers usually take up a contract to kill.
4.predators have specialized organs for attacking their prey, killer uses harm instruments for their mission
I think it would be what's the difference between a predator and a serial killer. This question has many ways to answer. I am imagining that the predators here are like those in the movie predator.
Predators are humans who love to stalk his or her victims before killing the victims. They are very skillful hunters who love to hunt for a game. They usually plan out the whole plan before going hunting. Then finally if they see their victims, they would not simply just take a knife like what Micheal Myers in Halloween would do which is just blindly stab his victims. The predator would maybe observe what his/her victims does and imagine of his game and his killl number. Then when the time comes boom. The victim is neutralized and erase.
Killers, I guess they do things in a more boring way. Maybe a killer just randomly goes to a spot and wait for victims. No planning required. The killer carries a knife( guns are not legal in my country), then when someone unsuspecting comes, out comes the knife and the killer just slashes the victim like that of fruit ninja. I don't know if this is logical or not. Then the victim may try to scream and run, the killer s adrenaline rush increases chasing the victim and maybe stabbing the victim from behind and the victim falls on the floor. Trail of blood follows. The victim crawls. Sound scary saying something like this.
Predators is said for Animals that want to eat a smaller less powerfull animal. A killer would kill his pray too but just for fun.