Based on the paper towel clues, who did Sam Westing accuse of taking his life, and why did he accuse this person?

The clues on the paper are as follows:
FOR PLAIN GRAIN SHED (Chris Theodorakis and Denton Deere)
SEA MOUNTAIN AM O (Turtle Wexler and Flora Baumbach)
FRUITED PURPLE WAVES FOR SEA (James Hoo and Grace Wexler)
HIS N ON TO THEE FOR (Doug Hoo and Theo Theodorakis)
SKIES AM SHINING BROTHER (Sandy McSouthers and J.J.Ford)
GOOD GRACE FROM HOOD SPACIOUS (Sydelle Pulaski and Angela Wexler)
THY BEAUTIFUL WITH MAJESTIES (Berthe Crow and Otis Amber)
OF AMERICA AND ABOVE GOD (Jake Wexler and Sun Lin Hoo)
The residents of the Sunset Towers wrestle for quite a long time with their clues, but they eventually figure out that the words can be rearranged to form the first verse of "America the Beautiful." This is an important song for Westing because he took very active roles at the Fourth of July celebrations.

A great patriot, Samuel Westing was famous for his fun-filled Fourth of July celebrations.

Unfortunately, the clues are technically missing pieces of the song's first verse. The missing pieces are "ber," "the," "erica," and "crow." Stitch those pieces together, and they spell "Berthe Erica Crow." This casts suspicion on Crow, but it is just Westing throwing in some misdirection. He is likely testing the residents and the potential heirs. Westing made it clear that what was important was what they do not have.

It is not what you have, it’s what you don’t have that counts.

This particular gem of a clue comes from the tenth part of the will, and it is meant to tie back to the third part of the will, which says the following:

The estate is at the crossroads. The heir who wins the windfall will be the one who finds the . . .

When this part of the will was read, Sandy shouts "ashes" as a joke to finish the sentence. It turns out that Sandy is Westing, and he is taking an active role in manipulating the game at this point. Everyone assumes that they just did not hear the word that was supposed to be read. Turtle figures out that there never was a word there in the first place. She then realizes that if you read the will and finish section three, the very next word is "fourth." Everyone assumes that the "fourth" just signaled the next section of the will. Turtle figures out that the sentence's missing word is actually the next word in the reading of the will. The sentence should read as follows:

The heir who wins the windfall will be the one who finds the fourth!

Turtle uses that clue to then figure out the four men that Westing is disguised as.

Each pair of heirs in The Westing Game receives a set of clues typed on Westing Superstrength Paper Towels that they must solve in order to have a chance at winning the game. The combined clues can be arranged to compose most of the first verse of "America the Beautiful," with the exception of four missing portions: ber, the, erica, and crow. This omission directs suspicion towards Berthe Erica Crow, the cleaning woman at Sunset Towers who happens to be the former wife of Sam Westing.
Crow is a red herring intended to distract from the task at hand; the clues "it is not what you have, it's what you don't have that counts" and "the heir who wins the windfall will be the one who finds the fourth" ultimately lead Turtle to solve the mystery, unbeknownst to the other heirs. Sam and Crow both carried guilt following their daughter Violet's suicide, but the conclusion of the game is designed to bring closure to a sad period from the past, ensuring that Crow's finances are stable and Sam's forgiveness is demonstrated.