I doubt it. Most likely a homegrown psycho.
Unfortunately we have our share. Create a make believe world where there is no God - and that people are just animals - and sure, do whatever your mood tells you that day. This was also the Columbine shooters worldview (which is why they particularly sought out Christians to kill).
I suspect it is more of an issue with Santa Cruz than illegal aliens. Deny God, and the Bible, and you reap what you sow.
Psalm 9:17 The wicked shall be turned into hell, and all of the Nations that forget God.
This thread began yesterday:
Missing Santa Cruz 8 year old girl was raped and strangled (by illegal alien?)
We'll see what is revealed, though I've been sharing your doubts and also think that if he is indeed here illegally, there'll be an article with more substantial evidence sooner or later.