There are the homeless like this girl that deserve the compassion and understanding,  yeah some of them choose to live on the streets.......that's their world and the one that they feel like they are accepted and fit in to without judgement and they feel like they are happier living that life.  But there are others in that same subculture who prey on others.   I've witnessed a couple of gang type fights where it was all homeless people who hang out downtown.  Some of those people are dregs of the earth  others are not.   And when you live outside of it, it's sometimes hard to judge who are  the good guys and who are the bad guys in the homeless community unless you know someone personally. 
And actually no one knows whether it was another homeless person who killed them or if it was someone who is preying on the homeless.
It's sad all around.