Animal in suburban city killed a chicken - how to keep other hen safe?

[Sassy Hen]

Sometime during the day today my friend’s 3 year old white silke hen was killed by an animal of some sort
Right now they have one hen (also white silkie) and since they don’t know exactly what happened they aren’t sure how to prevent this from happenning again. If anyone knows anything or has advice, it would be much appreciated.
They let their hens free roam around their fairly large property. They have access to their enclosed coop area at all times. Their deceased silkie was in the yard with feathers strewn across the grass, so they are a little confused as to why she did not retreat to her coop. She was killed sometime late morning, so raccoons and the like are an unlikely cause.
Something interesting/strange: the other silkie was sitting behind the coop, so they’re considering that a wild animal entered the coop?
Again, if anyone has any advice, it would really be appreciated.

 

[Tonyroo]

A cat or possum can easily kill a silkie.

 

[RoostersAreAwesome]

It could have also been a hawk. I live in the suburbs and there are lots of hawks, so I only free range my chickens when I can supervise them (it’s easier when you have a small yard).

 

[McChooky]

The absolute worst predator for killing chickens & leaving them where they die are dogs. Predators don't usually kill for sport ,they usually eat part of it or carry it off to eat later.

 

[Sassy Hen]

Thanks for the information!