The prosecution

Hearings of witnesses confirmed almost everything that had been related in the local press.^[5] Eyewitness James M. McArthur, who had brought Muybridge to the authorities, told how Muybridge had calmly and spontaneously discussed how he had planned everything, had no regrets and believed men of family would understand his choice. Muybridge had arranged his affairs in case he himself would get killed or lynched, but made sure that Larkyns had little chance to defend himself.^[8][9]

The defense argued against the insanity plea. It was impossible that Muybridge had gone insane after receiving proof for his dishonor, if he afterwards had quietly conversed with witness Harry Edwards and informed about business options.^[10] In his closing address, Stoney stated that there was not the least conclusive evidence of insanity. The expert witness for the defense had argued that Muybridge had not been insane and the conclusion was incontrovertible. Muybridge was either guilty of murder in the first degree or should be set free. By law, adultery was no justifiable provocation for murder. The law provided penalties for crimes if proven and Larkyns had received no trial from Muybridge. Muybridge had deliberately committed the murder and ignored the law, without any irresistible impulse or insanity as an excuse.^[11]

The defense

Muybridge's attorneys intended to prove that Larkyns had been a man of bad character and deserved his fate. Larkyns seduced Mrs. Muybridge under false pretenses, claiming to be a married man and luring Flora to his lodgings. He boasted about it to friends. Learning about the depth of the deceit made Muybridge insane from anger, to the point that he passionately decided to kill the destroyer of his happiness, loving his wife deeply, only living for her. Muybridge had been prone to insanity since a stagecoach accident in 1860, his hair had turned grey in three days and he never was the same ever since.^[8]

Susan C. Smith, a maternity nurse who was well acquainted with the Muybridges and with Larkyns, testified that she had known about the relationship between Mrs. Muybridge and Larkyns. She gave several examples that implied that the couple thought that Florado was actually Larkyns' son. She had received letters from Mrs. Muybridge and Larkyns that proved their ongoing affair and had offered them to Muybridge to convince him to pay a debt. Muybridge had found the baby picture with "Harry" on the back at her place. The letters and the picture were introduced as evidence.^[8]

Muybridge testified about how he had sustained head injuries in a stagecoach accident in July 1860. He had been unconscious for nine days and woke up with double vision and loss of taste and smell. The problems persisted fully for three months and in a lesser extent for a year.^[12]

All the witnesses related incidents that illustrated Muybridge's eccentricities. Mrs. Smith told how one day Muybridge came home, looked happily at his wife and child, then suddenly got confused over who had fed the canaries. After being told that he himself had done so, he replied "Ah dear me, I feel bad here sometimes" while pointing at his forehead. Rulofson referred to a picture of Muybridge sitting on the edge of a rock in Yosemite, where he could easily fall 2,000 feet.^[13] Rulofson, portrait photographer Silas Selleck and several other friends and long-time acquaintances testified that Muybridge's personality was dramatically changed after his 1860 stagecoach accident and consequent stay in Europe. He had turned from a genial, pleasant and quick business man into an unstable and erratic photographer.^[8] After the accident, Muybridge had occasionally been very violent and excitedly rude.^[11] McArthur related how Muybridge had been very cool and collected since right after the murder and had taken hold of a glass steadily when he was allowed to join the people having drinks at the Yellow Jacket ranch. This calmness had surprised McArthur, but he had not noticed anything unusual about Muybridge otherwise. Rulofson was called back and related that Muybridge had fallen about his neck and wept and had said he was very sorry, but straight afterwards recollected himself and denied the excitement. Rulofson had only experienced such paroxysms with Muybridge when it concerned his wife and his honor.^[11]

Dr. Shurtleff, an expert on insanity, believed that the homicide was premeditated and that Muybridge had been aware of possible consequences. The act had seemed justified to Muybridge and didn't come from an irresistible impulse, but from a passion. There were no reasons to believe that Muybridge was insane.^[11]

In his two-hour closing address, W.W. Pendegast's asked the jury, at the request of the defendant, to either acquit Muybridge for any crime or to send him to the gallows, like the district attorney had proposed. Although the law did not offer a statute "permitting a man to slay his injurer. But, law or no law, every fiber in a man's frame impels him to instant vengeance" at all cost. Muybridge had not just killed Larkyns for revenge, but also to protect his wife against the debauchee who kept pursuing her, as evidenced in Larkyns' letter.^[10]

Verdict

The judge gave the jury four optional verdicts to choose from: "guilty of murder in the first degree" punishable by death, another conviction for murder with punishment by lifelong imprisonment, "not guilty" or "not guilty on account of insanity". He also pointedly instructed the jury that even if Larkyns had seduced Muybridge's wife, the defendant was not justified to take the law into his own hands. After a long first jury meeting, they stood five for conviction and seven for acquittal, before retiring for the night at 23:00. The next morning they arrived at the agreement that the murder was justified, but they could not immediately decide whether or not Muybridge had acted out of insanity. The eventual acquittal was explained by arguing that if their verdict was not in accordance with the law, it was in accordance with the law of human nature. They felt they could not punish a person for doing something that they themselves would do in similar circumstances.^[14]

Upon hearing the verdict, Muybridge burst out in wordless moaning and convulsive, childlike weeping and fell into Pendegast's lap. The frightful display of emotion was said to have been "seldom, if ever, been witnessed in a court of justice". Muybridge was subsequently set free.^[14]