Aaron Burr on the Lam

Burr Blog -- Paper Little

As part of its Aaron Burr correspondence The Gilder Lehrman Collection holds a pair of previously unsolved ciphered letters.  (Their website presents the two as linked, but the ciphers are, in fact, distinct and separate.)  One of these ciphered letters–written to Burr’s son-in-law Joseph Alston under cover to the family friend named Charles Biddle in Philadelphia–dates from the period shortly after Burr’s pistol fire fatally wounded Alexander Hamilton on 12 July 1804.  What was the message that Burr took such pains to transmit secretly at this dramatic juncture in his life?  The answer follows.


The total number of unique symbols present in Burr’s cipher to Alston is twenty-four, two symbols short of the twenty-six letters in the modern English alphabet.  This near concordance suggested to me that some form of substitution cipher was being used.  Given that Burr was corresponding with his son-in-law at a distance, and that opportunities for prior consultation were limited, the cipher form also seemed to me likely to be a relatively simple one.  And so it was.

To crack the cipher I began, in the usual way, by constructing a frequency table of symbols.  Then, using William F. Friedman’s Index of Coincidence, I tested to see if the cryptogram was likely to be either mono or polyalphabetic.  The I. C. test compares the theoretical I. C. for English language plaintexts (which Friedman derives as 1.73) with the I.C. of the particular cipher text.  For a particular text Friedman’s Index of Coincidence is defined as the ratio of PHI(o)/PHI(r), where PHI(o) = sum N(N-1) and PHI(r) = .0358N(N-1).  (The constant .0385 is the decimal equivalent of 1/26.)  In the case of Burr’s cipher text, I came up with an I. C. of 1.60 ≈ 1.73.  This result suggested a monoalphabetic substitution cipher.

There are several time-tested methods of cracking a monoalphabetic substitution cipher.  The choice of attack is often dictated by the presence of telltale patterns within the cipher text.  The distinctive repetitions of one such pattern (10 8 IX IX 10 I) made it a likely place to start.  Using Jack Levine’s A List of Pattern Words of Lengths Two Through Nine, I searched for six-letter words of the form a b c c a d.  The word LITTLE seemed a likely fit, especially as Burr’s followers were often called “The Little Band.”  By recourse to the frequency table I generated (which indicated likely solutions for high-frequency symbols) and some trial and error, I was able to reconstruct the plaintext and most of the key upon which it was based.  A transcription of the deciphered letter is available here (the website actually includes some deciphered text, suggesting the cipher was previously solved by someone, but the plaintext is garbled).

Historical Context and Significance

Alston’s docketing indicates that Aaron Burr sent the cipher letter under cover to Charles Biddle on Friday, 20 July 1804.  In the days since Alexander Hamilton’s death, a coroner’s jury had been empaneled to consider whether Burr and the duelists’ seconds should be charged with murder.  On that particular Friday Aaron Burr, who was holed up in his Richmond Hill estate in New York City, claimed to be awaiting the jury’s findings to “determine my Movements.”

Burr Blog -- Richmond Hill

But before its next meeting scheduled for Monday the 23rd, Burr had fled the city.  On the late evening of Saturday, 21 July, he and John Swartwout, the federal Marshal for the District of New York and a loyal Burrite, were rowed in a barge across the Hudson River to Perth Amboy, where, the next morning, Burr’s friend Commodore Thomas Truxtun found Burr’s barge anchored at the foot of his lawn.  After the men breakfasted together, Swartwout returned with the barge to New York City; Burr, after spending a night at Truxtun’s estate, borrowed some horses and a carriage from his host to begin a trip across New Jersey.  The fugitive arrived in Philadelphia on Tuesday, 24 July, where he contacted Charles Biddle, who had previously offered him sanctuary.  Although Burr tried to keep a low profile, it was not long before he was recognized in the streets, and the city’s newspapers, Federalist and Republican alike, began to rail against him. (For Burr’s movements at this time, see Kline and Ryan, Political Correspondence and Public Papers of Aaron Burr, 2: 890; and Thomas Fleming, Duel: Alexander Hamilton, Aaron Burr, and the Future of America, Ch. 18.)

From the deciphered portions of the letter, it appears that Burr’s decision to flee New York City was made quickly.  On Friday the Vice President was asking his son-in-law’s advice on whether, in the event of an indictment for murder, to “stand” his ground or “go to Europe”; but before an answer could be received, Burr fled precipitously in the night.  Warmed, as he seems to have been on Friday, by the Little Band’s devotion, Hamilton’s killer clearly was unprepared to hazard the justice system in the prevailing political climate and before judges appointed by Federalists or, probably worse, Burr’s Clintonian Republican rivals.  As Burr had told Charles Biddle in a letter of 18 July 1804, “You can judge what chance I should have in our Courts on a trial for my life though there is nothing clearer to a dispassionate Lawyer than that the Courts of this State have nothing to do with the death of Genl. H——-“ (Kline and Ryan, Political Correspondence and Public Papers of Aaron Burr, 2: 885-86).  These misgivings ultimately short-circuited the impact of any advice Alston might have offered his father-in-law about “standing” or “going.”

All things considered, the cipher letter to Alston adds little to our understanding of the denouement of the famous duel beyond corroboration that Burr was, at this dramatic juncture, less a man acting out his destiny than one reacting to the tide of events.

Next up: Burr meditates an invasion


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