That's true that motive, means, and method can shed light. We don't have any of that information though. We don't know where the cross was found, how it was found, who found it, what position it was in, whether it was on the ground, in something else, in the air, hanging, laying, sitting, leaning...we know nothing except what it looks like and it was found "at one of the crime scenes." We don't know if it got to wherever it got to accidentally or on purpose.
So -
- could it have been placed on purpose? Yes
- could it have fallen off accidentally? Yes
- could it have been at the body site? Yes
- could it have been placed on or near the body? Yes
- could it have been hanging on something nearby? Yes
- could it have been found not at the body site but in or near the backpack? Yes
- could it have a religious connotation? Yes
- could it have nothing to do with religion? Yes
- could it be something meaningful to the perp? Yes
- could it be something not meaningful to the perp? Yes
- could it have been worn around the neck? Yes
- could it have been carried in a pocket? Yes
- could it have been on a keychain? Yes
- could the perp be using it to taunt police? Yes
- could the perp be using it to show remorse? Yes
- could the perp have no special secret message and the item just fell off or out? Yes
- could it have been on a chain? Yes. A leather type necklace? Yes.
With the fact that we know nothing, any of those scenarios and many more are possible.