The most important expert was Nathan Keep, the dentist who had made Parkman's false teeth. Those teeth were unusual because of the way Parkman's lower jaw jutted out.

Dr. Keep testified he recognized the most significant evidence found at the crime scene: false teeth. Keep had made them for the murdered doctor. That evidence was crucial for the case. It was also the first time dental evidence was used in a trial.

But prosecutors still had to deal with two huge issues. They had no actual body identified as Dr. Parkman. And, how were they going to tie Dr. Webster to the crime? Webster had denied any wrongdoing and there were no eyewitnesses. The janitor's testimony was crucial, and he was unshakable on cross examination. (These are notes from George Bemis, the chief prosecutor, regarding the janitor's testimony.)

The prosecutors faced a final battle. Even though their circumstantial evidence was overwhelming, they still had the problem of the corpus delicti rule. They had great secondary evidence, but the primary evidence - the body - was missing. How the Judge instructed the jury would make or break the case. Here is the most telling part of his charge:

It has sometimes been said by judges that a jury never ought to convict in a capital case unless the dead body is found. That, as a general proposition, is true. It sometimes happens, however, that it cannot be found, where the proof of death is clear. Sometimes, in a case of murder at sea, the body is thrown overboard on a stormy night. Because the body is not found, can anybody deny that the author of that crime is a murderer?

The instruction was just what the prosecutors needed. It took the jury less than three hours to convict Dr. Webster. (Scroll at least 3/4 down this very long link to get to the story of the Parkman murder.) Judge Shaw passed sentence: Death by hanging.

Dr. Webster tried to save his own life by filing an appeal. That didn't work. He tried to save his life by petitioning the governor for clemency. That didn't work either. Only then - after he had exhausted all the legal means to save him - did he confess. But therein lies the ultimate irony. Webster's confession was strongly supportive of temporary insanity. Had he told the truth at trial, he would likely have avoided the hangman's noose. Instead, he was executed on August 30, 1850.

Webster's family received help from a most unlikely source after his trip to the gallows. Dr. Parkman's widow raised funds to help Webster's wife and children.

A Harvard law student who attended the trial thought the verdict against Webster was wrong. Here's his opinion.

Some 20th century writers think Judge Shaw went too far in his jury instruction.