An early forensic scientist, Haines testified in a number of sensational trials, including those relating to the Haymarket bombing of 1886, the disappearance of Adolph Luetgert's second wife Louisa in 1897, and the suspicious deaths in multimillionaire Thomas Hunton Swope's family in 1909.

[4] He was acclaimed for both the quality of his teaching and his kind and sympathetic manner:[5] It was the usual experience of students from other schools who had labored memorizing endless "equations" that his clear analysis changed chemistry for them from a difficult "blind" subject to a pleasant and profitable one.

His kindness and almost feminine gentleness endeared him to fifty classes of students, and as a member of the faculty his influence moderated the asperities during many strenuous years.

Haine's contributions included a chapter on "General Principles of Toxicology", which described common poisons, their symptoms and treatment, and best practices for postmortem examinations.

[4] Haines was a pioneer in adapting medical techniques from the laboratory for application to forensics investigations and the presentation of courtroom evidence.

[1] His unswerving adherence to the facts, revealed by his analyses and tests, the rigid care and thoroughness with which these analyses were conducted and controlled, combined with a remarkable faculty of explaining scientific facts and methods in language intelligible to those wholly unacquainted with chemistry or medicine, made his testimony most convincing to judge and jury and a formidable problem to the cross examiner.

The shrewder members of the bar early discovered the wisdom of refraining from the cross examination of Dr. Haines, for it almost always resulted in giving added force to his testimony.

Some of the trials in which his cross examination was conducted by distinguished lawyers, who vied with him in quiet, courteous deportment, will long be remembered for their masterly, delightful word-fencing.

He discussed fragments of the exploded bombs, the only physical evidence to be presented at the trial, and their similarity to materials found in the possession of one of the defendants.

Anyone who was party to the plan could be held responsible for its consequences under Illinois law if it could be shown that the bombing was premeditated–which was murder in the Haymarket case.

Haines argued that commercial lead samples did not include tin and suggested that the exploded and unexploded bombs had been made from a consistent "recipe".

"[1] Haines testified that the remains found by the police were physically consistent with the suspected method of disposing of Louisa's body.

Haines reported that he had tested this by boiling down three cadavers in solutions of potash, a substance that Luetgert had purchased prior to Louisa's disappearance.

[1] In late 1909, several deaths occurred in the home of Thomas Hunton Swope, a Kansas City bachelor who had become a multimillionaire in real estate.

Bennett Clark Hyde carried out the blood-letting and insisted on bleeding him heavily, in spite of objections from nurse Pearl Kellar and Dr. George Twyman.

Frances and William's sister Margaret also took a pill at Hyde's instruction and went into convulsions, but she recovered with treatment from Dr. George Twyman.

[17][18] Hyde appealed the decision, and the Missouri Supreme Court overturned the verdict on procedural grounds on April 11, 1911 and called for a retrial.

[18][19] Hyde's wife Frances supported him through extensive court proceedings, which included at least two mistrials, one possible bribery attempt, and additional litigation over who would pay the cost of the prosecution.

The State of Missouri and Margaret Swope are estimated to have spent $250,000 pursuing Hyde's conviction, but the charges were dropped on April 9, 1917 and he was released.