Y'ARR! THERE BE SPOILERS AHEAD, MATEY!
Ok, those of you who know me know I watch "Downton Abbey" with my lovely wife. It's something that we just do. We like the sets, the props, the actors, the story...the whole thing.
Now, recently, one of the "bad guys," if you will, on the show ended up dead. (And good riddance!) Anyway, her character name was Vera Bates, and there's a lot of discussion about how she died and who is responsible for it.
In both cases, we have little to work with. Let's look at the poison first.
According to the plot-line dialog and the wiki page dedicated to the show, all we know is that she died by being poisoned with "rat poison."
This could be many substances...a whole run of possibilities; however, the episode of her demise takes place in 1918, which limits things for us greatly.
By looking at the condition of her body as she was found (with voice-overs) we see that she seemingly dropped dead in a hurry--practically instantly. This can't happen with Arsenic, so it's out. Warfarin wasn't available until after WWII, so that's out too.
What I think it was is simple: white powder, possibly crystalline, and fast acting. This, to me, says Cyanide.
Secondly, who could have done it--and motive?
Well, here we have more options.
John Bates -- the husband. He hates her, and wants her out of his life so he can go be happy with Anna. Plenty of motive. Sadly, he foolishly did mention to the Earl that he'd like to see Vera dead (more or less.) And where did that scar on his left temple come from?... We don't know... For all we know, Vera could have attempted to slap him as he left, or threw a cup at his head as he turned his back on her once and for all.
Anna -- the rival for John's love. She, too, would like Vera out of the way, and benefits from her being gone by getting John all to herself.
Vera Bates -- yes, she could have "offed" herself purposefully. She had recently been confronted by Sir Richard about blabbing the story of the Turk who died in Mary's chamber. As a result, she couldn't use that story any more to threaten John's life, but if she ended up dead, under odd circumstances, the blame would logically be pointed at John....spoiling the fun from beyond the grave! We don't know everything that was going on in her life--perhaps Vera had been diagnosed with a rare, fatal illness, and the "real" reason she wanted John around was because she didn't want to die alone; but when John chose Anna over her (who the hell wouldn't?) she felt the best option was to end her life on her own terms, in some kind of painless manner and with what remained of her dignity remaining. Staging her own death to look like someone killed her is just icing on the cake that screws John and Anna's plans up (short term, at least until the truth comes to light.)
O'Brien -- She asked to borrow some baking powder...a white substance. Something easily used to cover an equally white poison. Why would she do it? The story Vera could blab would harm the Grantham name, and lately she's been awfully protective of Cora since the whole "slip on the soap" incident.... Just protecting her own, perhaps?
Sir Richard -- He bought the story from Vera under a draconian contract to prevent the tale from leaking out, but when Vera seemed that she might go elsewhere or leak the info--he had to do something to (a) protect his revenues from a story he owned, and (b) he was, at the time, sill engaged to Mary--and this leak would have ruined her name, possibly the whole family's, and even his for being associated with such a wonton harlot.... Protectionism at its finest. Also, keep in mind that the actor who portrays John Bates said in an online forum about this very option called the people to brought it forward (and there were a lot), "Brilliant." This is by far the most popular opinion--but as we know, dramas and their writers love to make the murderer someone other than the most obvious choice.
Lord Grantham -- John "threw himself on his sword" to protect the family's name. He, being an honorable fellow, could have chosen to pay dear Vera a visit to repay John for the kindness and loyalty shown earlier. Highly unlikely, but possible.
The rest of the cast would be practically impossible as the killer. So we'll leave them out entirely.
For my money, I believe that either Sir Richard did it, or Vera offed herself. But which of these is the more likely?
If you're going to kill someone, and you're wealthy, you don't get your hands dirty so the trail cannot be traced back you. Sir Richard would know this, so he wouldn't go personally; however, if he sent agents, this opens up a potential can of worms because all it takes is one drunken moron to open up to the wrong person saying who, why, how... And Sir Richard goes to the gallows. He's a careful man, and would take massive precautions. As a result, he now, to me, seems highly unlikely.
This leaves Vera killing herself and setting it up to blame John--thereby ruining his relationship with Anna. I now choose this option because I don't think Bates did anything, he's a meek man with honor....killing a wife, no matter how she deserves it...just isn't "him," if you get the meaning. Sir Richard would stand to lose far too much if he was ever implicated. But Vera was a witch of a woman, and I wouldn't put it past her at all to do this as a parting "kiss my ass, John!" as she slipped her mortal coil.