Quote 10
There was nothing to wash out – no stain of any kind – no blood-spot whatever. I had been too wary for that. A tub had caught all – ha! ha! (8)
What exactly does the narrator use to do the dismembering? He makes no mention of disposing of the cutting implement. Is he being cunning, or did he just forget to mention it?
Quote 11
The officers were satisfied. My manner had convinced them. (9)
Has the narrator outsmarted the police officers, or are they hanging out with the narrator because they suspect him?
Quote 12
And every night, about midnight, I turned the latch of his door and opened it – oh so gently! (3)
If the old man leaves his door unlocked, it means he trusts the narrator, or (if he's bedridden) he might not have a choice. Either way, this is why we don't go to sleep until well after midnight.