The killing of the venerable Captain White was so mysterious and frightful that it attracted widespread attention before Senator Daniel Webster stepped on the scene. But his consent to appear for the prosecution gave it unprecedented notoriety.

In the summer of 1830, Webster, in his forty-ninth year, was at the absolute height of his fame—the Cicero of America, the matchless orator of the Dartmouth College Case, the Plymouth Oration, and the more recent Reply to Hayne, and not yet the perennially disappointed candidate for the Presidency. He had been elected in June, 1827, to the U.S. Senate.

Webster had had his own personal sorrows as well as his public triumphs. In January, 1828, his wife of twenty years, Grace Fletcher Webster, died after a painful illness, and his second wife, Caroline Le Roy, did not have an equally restraining influence upon him. Webster, always a free spender, lapsed deeper and deeper into debt.

In January, 1830, a bridegroom of only a few weeks, Webster reached his eloquent zenith in his Reply to Hayne, and from that moment he was regarded as the outstanding spokesman for the Union. When the twenty-third Congress closed its first session on May 31, Webster made his way, in the slow fashion of those days, back to New England. While in the capital, he had read of the White murder; and his friend, Justice Joseph Story, had written him from Cambridge giving some of the gory details. Stephen White, the man who invited Webster to enter the case, was Captain white's nephew and had married Judge Story's sister; White's daughter later married Webster's son, Fletcher. Many ramifications of this crime gave it the aspect of a family affair.

Harriet Martineau, in her Retrospect of Western Travel (1838), told how the rusticating statesman was persuaded to assist in the prosecution of the Knapps:

“A citizen of Salem, a friend of mine, was deputed to carry the request.… Mr. Webster was at his farm by the seashore. Thither, in tremendous weather, my friend followed him. Mr. Webster was playing checkers … My friend was first dried and refreshed, and then lost no time in mentioning business. Mr. Webster writhed at the word, saying that he came hither to get out of the hearing of it. He next declared that his undertaking anything more was entirely out of the question, and pointed, in evidence, to his swollen bag of briefs lying in a corner. However, upon a little further explanation and meditation, he agreed to the request with the same good grace with which he afterward went to the task. He made himself master of all that my friend could communicate, and before daybreak was off through the woods, in the unabated storm, no doubt meditating his speech by the way. He needed all the assistance that could be given him, of course; and my friend constituted himself as Mr. Webster's