Breaking into Snape's office

[clio44a]

No: HPFGUIDX 32872

Couple of days ago Eloise posted something on security in Hogwarts. 
That made me think about the time when Barty Crouch aka Mad-Eye Moody 
breaks into Snape's office (same night as Harry goes into the 
prefect's bathroom) in GoF.

I wonder what he actually wanted there. For Moody-the-paranoid it 
would make sense to search the office of a known Ex-Death Eater. But 
Moody is Crouch. So why would Crouch go into Snape's office?

Would he look for evidence if Snape is still on the Dark side? What 
evidence would that be? I mean he can't hope to find Snape's old DE 
mask in a drawer or a file labeled Spying for Ddore 1979-'81, can he? 

I cannot imagine Snape would keep any material concerning his DE days 
or his service to Ddore in his office. His office is not a particular 
safe place. It was broken into by H/R/H in their second year and 
Snape has student visitors in there, like Harry on occasion (not 
voluntary, but he was there). He even leaves Ron and Harry alone in 
there for 10 min in CoS. So secret files, DE toys or poisons can be 
ruled out from being in the office, I think.

Maybe Croutch was looking for potion ingredients in the office. Snape 
mentions gillyweed and boomslang skin to be stolen when he threatens 
Harry with the Veritaserum in GoF. We know that boomslang skin is an 
ingredient for Polyjuice Potion. 

H/R/H were nicking boomslang skin from Snape in their 2nd year 
because they couldn't get it from anywhere else, if I remember 
correctly. Assuming Croutch brews his Polyjuice Potion himself, which 
would hold a high risk for him to be discovered,why would he risk 
stealing from Snape's stores? Snape would find out eventually that an 
ingredient for Polyjuice Potion is missing, and Crouch can't afford 
to give away any hints that there is somebody brewing Polyjuice 
somewhere in the castle.

Crouch, unlike R/H/H could easily go to London to buy boomslang skin 
without anybody questioning him about him going there. And while he 
was there, why would he not buy complete Polyjuice Potion? Wouldn't 
that be less risky than to brew it himself?

And another thought about Crouch breaking into Snape's office: Why 
wouldn't he hide his tracks better? Snape says the door was ajar and 
the torches lit. Wouldn't you use a lumos spell on your wand if you 
were searching one's office at night? IMHO either Crouch felt 
completely safe to search the office (had Ddore really given Moody 
premission to do so?) or he wanted Snape to know someone was in his 
office.  
    
So what do you guys think he was really doing in Snape's office that 
night?

Clio,
who always gets confused when she starts thinking about something too 
hard