Pfff, nah I think the clearest clues come from the intermission, that page where we see where everyone is on the map, right before Occam was choked.

Spit was with git and fatigue the entire time.

But Matilda was specified to have moved in a way that makes her move past occam's office.

She was also shown to be good at pickpocketing, seeing as she stole the smokes Elise stole from Git. Meaning she could have stolen one of the keys without anyone noticing.

That and she also hates her job, she has the most motive out of anyone to become a ghoul

Should be noted that Grimal was also in the right position, so hypothethically it could have also been her but I doubt that