[null and void]

The guy in the car could have been an immoral, uncaring piece of garbage.

Or he could have been afraid, afraid that the knife guy was still lurking around.
Or he just could have been in shock over what he saw. Untrained folks in shock often do odd things.

Lots of possibilities here.

Or he could have been afraid of contracting AIDS from exposure the the blood of a random San Fransisco stranger?

Even the cops and paramedics won't touch a bleeding victim without gloves. Perhaps he didn't have gloves at hand?

[mware]

Wonder if this was a targeted attack and not some random thing.