Empathy for Strangers

Why is it that we feel a sense of sympathy or sadness whenever we hear of a passing of someone we don't know personally?

Are we saddened because of a loss of a life, that we can relate to the feelings of the family of the deceased, of the things that can no longer be done/enjoyed by the deceased, or is this just a normal human reaction called empathy?

If the departed happens to be someone we know personally, then would our reaction be the same? I suppose not, as past memories spent with that person would summon a stronger emotional response and attachment. Plus the fact that we (might) have spent a good deal of our lives with the deceased is another factor. But still, going back to my original question, why then would would our hearts sink a little, and our eyes slightly squint when we learn about the passing of someone we have no connection whatsoever to?

It probably wouldn't be normal if we didn't feel so, but I'd like to know the science behind this. Probably what makes this hard to understand is how different people deal with the issue of death.

A definite answer I will probably not get, and Googling did not yeild sufficient clues. A couple of sites were quite helpful in understanding grieving following a person's death.