Remix in comments flagged an important clue about the author of the Ricin Letters. The line...

letterlinepoem.jpg from a poem, "A Display of Mackerel", from a collection by poet Mark Doty. The poem appeared in Atlantis, a 1996 collection of poems that Doty wrote after the HIV-related death of his partner in 1994.

They don’t care they’re dead
and nearly frozen,

just as, presumably,
they didn’t care that they were living:

So whoever wrote the letter knows—and plagiarizes—his gay poets.

More from Doty's wiki page:

In 1989, his partner Wally Roberts tested positive for HIV, which drastically changed Doty's writing. Roberts's death in 1994 inspired Doty to write Atlantis, and Heaven's Coast: A Memoir also deals with this subject. In 1995, he won the ₤10,000 T.S. Eliot Prize for Poetry, the first American poet to have done so.

markdoty.jpgHe has written twelve books of poetry and three memoirs. Firebird told the story of his childhood in the American South and in Arizona. Dog Years was a memoir of the lives of two of his dogs who Doty had while dealing with the death of his lover and the devastation of 9-11. Louise Erdrich praised the book as being "about dogs, that is to say, about everything we cannot talk about... the 'unsayable' about our relationships with animals, and about unspeakable times of loss, Dog Years is not a dark book. It is illuminated from within by gorgeous wonder." Dog Years is the winner of the 2008 American Library Association Stonewall Book Awards Israel Fishman Non-Fiction Award. His last book of poetry Fire to Fire: New and Selected Poems won the 2008 National Book Award for poetry.