Once upon a time, Dexter knew how to fade into the background. He knew how to be the quiet lab guy who took his samples, analyzed a bit of blood spatter and went on his merry, serial-killing way without anyone being the wiser. These days, everyone seems to have his eye on him, trying to figure out - as Isaak put it - what kind of monster he is. And rather than ducking further into the shadows, as one might expect he should do, waiting out the suspicion until things die down, Dexter seems to be knee-deep in the thick of things. It's just a matter of time before it all blows up.
Do what you do.
Sal Price is dead. But before he met his demise in a manner so obvious, it's a wonder he didn't see it coming, he was snooping around Hannah McKay, trying to fill in the blank pages of the book he's writing about her. That brought him to the street outside Hannah's house just as Dexter was dropping her off after their winter wonderland of kill-table sex. Things may not have gone the way Dexter planned, but Hannah appeared to adjust from being almost-murdered to being in a semi-relationship with her would-be killer. I guess when you spend part of your adolescence hanging around a murderer, it's easier to handle 180's like these.
Sal's scenes were divided between narrow-eyed moments with Dexter and Hannah, wanting to get whatever information he could from them, and hanging around Deb, dropping cheesy lines on her but also sharing updates on the Hannah McKay case. Deb got Hannah's deceased husband's sister Laurie to agree to exhume her brother's body so they could test his tissue for poison, only to discover that - on Hannah's orders - the body hadn't been embalmed , so there was no tissue to test. Dead end there. But then Hannah gave Deb another body to examine: Sal Price.
Sal's trying to prove Hannah's a murderer, so you'd think he'd be wary about putting things in his mouth while at her place. Or even being around her at all, really. Of course, he revealed his oral fixation to us earlier in the episode when chatting with Deb, so the pen thing didn't entirely come out of nowhere. Hannah was also aware of his mannerisms and used that to her advantage by poisoning his pen, figuring it'd kick in while he was driving and he'd die in a car accident. And after tearfully confessing to stabbing the beach-woman to death - a crime she can't be punished for due to her immunity - and implying in her confession that it was an act of fear or hysteria or whatever, she sent him on his way, not realizing Dexter's house was his next stop, or that the poison would kick in when he was with Dexter.
Because Sal knew Dexter and Hannah were now seeing each other, and that Dexter fudged the blood report to protect Hannah, Sal was trying to get Dexter to give him information on her. In turn, Dexter was doing his best to get rid of Sal once and for all, and his plan was blackmail. Maybe if he and Hannah had swapped notes, they could have worked on this together, but that doesn't really matter anymore.
Earlier, Dexter broke into Sal's place, stole a bunch of DNA, erased the Hannah files off his computer and left. When Sal dropped Dexter's house after visiting Hanan, Dexter told him he'd plant Sal's DNA on the murder scene of a murder victim Sal wrote a book about. No idea how he planned to do that, but again, it doesn't matter anymore. Sal yelled at Dexter and then died of a heart attack on the floor of Dexter's apartment.
I assume Hannah didn't realize Sal was talking to the cops about her being a murderer. She can't be that stupid as to kill the writer the same way she killed her husband and not think it was going to draw suspicion on her. The weird thing was, the toxicology report came up clear. Did I miss how they explained that? Did she somehow find a poison that doesn't show up in the blood work? Regardless, she's going to get away with this murder too.