The Shrieking Shack-did Snape have ulterior motives?

[jwcpgh]

No: HPFGUIDX 85699

So I was thinking about Tonks's wonderful defense of Lupin posts, 
and a thought occurred to me.  (Paramedics weren't necessary but it 
was a near thing.)  The night of the Shrieking Shack incident in 
PoA, Snape, as we know, appears in the Shack.  He tells the group 
that he found out what was happening when he went into Remus's 
office to give him his monthly wolfsbane potion and saw the 
Marauder's Map.  (PoA p.358 US). As soon as he grasps the situation, 
he goes tearing off to the Shack.   But wait a minute-what about the 
potion?  Why didn't Snape bring it with him?  He knew that Remus 
would be a lethal threat to HRH if he didn't take the stuff ASAP.  
(Yeah, Sirius too, but of course that wouldn't be an issue for 
Snape.) Severus had no way of knowing whether Remus had already 
transformed or not.  If he hadn't, he might at any moment, and 
really needed that potion.  And if Snape were at all concerned about 
HRH, he would have tried to prevent their coming to harm.  

If, on the other hand, Remus had already transformed, what did he 
think he could do against a werewolf and a murderer?  Why didn't he 
get some backup?

I can only infer that Snape was so eager to nail Sirius and Remus 
that he didn't really care if HRH were killed in the process.  
Doesn't say much for our boy Sevvie, does it?  And then he has the 
nerve to paint himself as HRH's selfless rescuer.  Nice, Snape, 
really nice.  

Laura, wondering who Snape would have gone after first if he had 
been in the MoM that night-Sirius or Bellatrix?