In the U.S. legal system, the prosecutor must prove their case “beyond a reasonable doubt.” The defense attorney is not required to prove that the defendant is innocent because the defendant is presumed innocent; the burden of proof falls on the prosecution. The laws in each state are slightly different, so before beginning to prepare the defense, it would be necessary to consult the legal requirements in Mississippi at the time of Emily’s arrest.

One strategy to employ would be to question the admissibility of any and all evidence, depending on how it was acquired. The question you pose mentions that Emily is still living, and that is how she came to be on trial. No indication is made of how entry was gained to her home. Was a proper search warrant executed? That would be one avenue to pursue.

A second avenue would be to review the autopsy findings, if a proper autopsy was conducted to ascertain the date of death. If other people were living in the house, or had regular access to the house at the time Homer died, then any one of them could be offered as an alternate a suspect. Tobe, who was in the house constantly, is of course the most likely alternate suspect. The prosecution also needs to prove that the death was a homicide rather than accidental, which will be very challenging for them to establish.

How about the "innocent" narrator, who claims to be reflecting on all of this in flashbacks, implicating the whole town as being complicit in a passive-aggressive way of her death?  Maybe he isn't quite as shocked as he pretends to be!

And Homer himself was quite the loudmouth, apparently, and the center of attention.  Perhaps he swindled someone in town and paid the price. 

I agree with Amy that the need is to raise doubt, not erase it.

And, as to Tobe,  maybe he and Emily were closer than Southern society would allow.  They live together alone for years and years.  As Jeff points out, he takes off after the murder.  Perhaps love and jealousy compelled him to kill his rival.. 

There is the evidence of the men's toiletry set with Homer's initials engraved on it as well as the spot in her bedroom where he hung his pants and coat.  It is obvious that he was living in Miss Emily's home, and there is no way that would happen in the south during this time period without plans to marry. 

Perhaps he died of a heart attack or other means of natural death.  There is no proof that he didn't... :)  Miss Emily may very well have had rats, and there is no forensic evidence that shows his hair or bone tissue contained traces of arsenic.

You don't need to prove that Miss Emily didn't kill Homer as much as you need to put doubt in the minds of the jury that it is possible he died in some other manner.  There is nothing to prove beyond a shadow of a doubt that she did it.  The gray hair on the pillow next to his only proves that she slept in the bed with him...as anyone might do if he/she were in love with the person who once was the corpse.

Think of the points you would make if you were the prosecuting attorney, and then counter them.  One point you can make is that she was a truly gentile southern lady.  The prosecution will use this as evidence against her to suggest Emily killed Homer to protect her reputation.  You can use it to counter by saying because she was a truly gentile southern lady, murder is simply out of the question.  It is too base, too beneath her status.

Good Luck! 

Well, you are going to lose, but let's try anyway. There is Tobe. Homer Baron was seen nearly every day yelling at his black work crew using harsh, racially-driven language. He took off as soon as Emily died. That looks suspicious. Maybe he was distraught that a yankee would be no different than what he was used to.

Perhaps Homer drank the poison in a mistake. He did like to drink and maybe he mixed himself an arsenic and tonic.

..none of this explains the iron gray hair though.