Aaron Burr is the highest-ranking federal official ever charged with treason. His trial in 1807 resulted in an acquittal and helps explain why there have been few treason cases since then.

Like everything in Burr’s life, the trial was complicated. By the time it took place, Burr had served four years as Thomas Jefferson’s vice president, killed Alexander Hamilton in a duel in 1804, and been kicked off Jefferson’s reelection ticket the same year.

Biographer Nancy Isenberg unwound Burr’s life in her 2007 biography “Fallen Founder.” 

In it, she told how Burr helped create our two-party system by transforming New York’s Tammany Society into a political machine; he was a visionary in other ways, too, including women’s rights.

Unlike most founders, Isenberg wrote, “Burr did not toot his own horn, nor did he defend himself with an eye to posterity.” He lived a long life, but for more than a century vanished from history, she added, because neither his wife nor his daughter survived him and many of his personal papers were lost at sea.

By 1805, Burr was under indictment in New Jersey and New York for killing Hamilton. Both states eventually dropped the charges, but by then Burr had fled New York, moving between South Carolina, where his daughter lived, Philadelphia and Washington.

Next, the widowed ex-vice president headed west, where he hoped to parley connections with British and Spanish ministers into an ill-defined effort that was later labeled “the Burr conspiracy.”

Many believed Burr wanted to create his own Napoleonic empire in Texas and Mexico; others said his plan was to organize new territories and bring them into the union. A popular theory today is that he had both possibilities in mind and was keeping his options open.

During Burr’s travels in 1805 and 1806, he organized a small army of about 80 men and received promises of support from, among others, Andrew Jackson in Tennessee and Gen. James Wilkinson, commander of the U.S. Army at New Orleans. 

Wilkinson was a key figure who turned on Burr and became his chief accuser. No one knew at the time, but Wilkinson was also a paid agent of the Spanish government; he even kept a secret Spanish military uniform. The extent of Wilkinson’s betrayals was not fully known until the 1920s, nearly a century after his death, when government documents in Madrid, Spain, were uncovered detailing payments for his services.

Burr made no secret of the fact that he was organizing an army with plans to move into what is now Texas and Mexico. Before he could make a serious effort, Wilkinson provided Jefferson with a secret letter outlining his plans.

Jefferson jumped at the chance and got so personally involved that his predecessor, former President John Adams, rebuked Jefferson for publicly condemning Burr before he was charged and tried.

Adams was right. Burr’s guilt was not at all clear.

With Wilkinson’s help, Burr was arrested in February 1807. A series of legal proceedings followed in Richmond, Va., beginning in March and extending through August.

Overseeing them was U.S. Supreme Court Justice John Marshall. Although Marshall was a cousin of Jefferson’s, he was a political opponent of the president.

Burr’s defense team was a who’s who of early American lawyers and included Edmund Randolph, the nation’s first attorney general under George Washington, and Luther Martin, another founding father.

Despite Burr having traveled widely and recruited scores of men for his cause, the prosecution could not find two witnesses who would testify with firsthand knowledge of Burr’s treason, which is what the law requires.

The main evidence against Burr was the letter Wilkinson possessed, written in code and laying out Burr’s plans. But under cross-examination, Wilkinson revealed that the original letter, if there ever was one, no longer existed. He admitted the letter shown in court was in his handwriting, not Burr’s.

Burr was acquitted by Marshall. He was quickly retried on a lesser charge and acquitted again.

The damage to Burr’s reputation was permanent; he lived until 1836 but was never again a factor in American politics.