Who was responsible for Sirius' death?

[katmandu_85219]

No: HPFGUIDX 167349

I was reading the prank topic, and someone stated that Snape
was responsible for Sirius' death.  That started me to think.
Why would Snape be responsible for his death?  Isn't Sirius
Harry's guardian?  His God-father?
Wasn't it his duty and responsibility to come to Harry's
rescue? Not hide away, and leave the danger to others?
Shouldn't anyone with information on Harry's welfare come to
Sirius? Isn't he the responsible party?

Speaking as a mom, I would certainly have been there if it was
my son in danger.

katmandu_85219