And William Wirt, the junior prosecutor, delivered an address that would be memorized and delivered by later generations of schoolchildren, irredeemably befouling Burr’s reputation. After colorfully portraying the Blennerhassett family as living in a modern, island-bound Eden, Wirt painted Burr as the serpent entering the garden: “The destroyer comes; he comes to change this paradise into a hell; . . . he soon finds his way to their hearts. . . . The conquest was not difficult. Innocence is ever simple and credulous. . . . By degrees he infuses into [Blennerhassett] the fire of his own courage; a daring and desperate thirst for glory; and ardor panting for great enterprises, for all the storm and bustle and hurricane of life.”

Chief Justice Marshall, however, did not fall for such passionate oratory. In the longest judicial opinion of his career, he insisted that the prosecution could proceed only with evidence that related directly to the charge that Burr had levied war against the government on Blennerhassett Island. With no such evidence, the prosecution rested. The jurors who reluctantly acquitted Burr refused to proclaim him “not guilty” of treason. Instead their grudging verdict read that Burr “is not proved to be guilty under the indictment by any evidence submitted to us.” President Jefferson denounced the verdict, calling it “a proclamation of impunity to every traitorous combination which may be formed to destroy the union.” “Marshall,” wrote prosecutor Wirt, “has stepped between Burr and death.”

A furious Jefferson insisted that the prosecution resume, this time on misdemeanor charges that Burr’s planned invasion of Spanish lands had violated the Neutrality Act. If that prosecution failed, Jefferson assured Hay, it “will heap coals of fire on the heads of the judges.”

Fail it did, for largely the same reason as the first trial. In order to preserve the jurisdiction of the Virginia court, the prosecutors again alleged that the illegal actions had occurred on Blennerhassett Island. Although Burr plainly had intended an invasion of Spanish territory, no witnesses could place him on Blennerhassett Island. A second jury delivered a verdict of acquittal.

In both criminal trials, the prosecutors lacked the most powerful evidence against Burr. His traitorous proposals to the British minister would lie concealed in that nation’s archives for generations, while the prosecutors could acquire no testimony from Burr’s confidants. Many of them, as prosecutor Hay grumbled in a letter to Jefferson, “will never utter a word injurious to Burr.” Six of them faced the same criminal charges pending against Burr, so they had no interest in giving testimony for the prosecution.

One of Burr’s closest confederates, a mercurial German expatriate named Erich Bollman, had been arrested by General Wilkinson in New Orleans and shipped to Washington, D.C., to face treason charges. The prisoner insisted on meeting privately with Jefferson to explain Burr’s true intentions.

In a February 1807 meeting with Jefferson and Secretary of State James Madison, Bollman disclosed that Burr had intended to bring 6,000 men to New Orleans. (The U.S. Army numbered barely 3,000 at the time.) They were to seize the ships in the harbor as well as artillery abandoned by the French when they sold Louisiana. When General Wilkinson brought in U.S. Army troops, Bollman reported, the “corps of Burr” would invade Mexico via Veracruz, as Hernán Cortés had done almost 300 years earlier (and Winfield Scott would do 40 years later).

Jefferson briefed prosecutor Hay about Bollman’s disclosures, sending him an essay by Bollman describing Burr’s plans. To ensure that Bollman would testify against Burr, Jefferson enclosed a presidential pardon for Bollman plus several blank pardons that Hay could deliver to all but “the grossest offenders,” thus securing their testimony. Jefferson then revised his instructions: Hay could grant the pardons even to the grossest offenders if “the principal [Burr] will otherwise escape.”

Jefferson’s stratagem failed. Bollman refused the pardon, steadfastly proclaiming his innocence. Yet he also refused to testify, asserting his constitutional right against self-incrimination. Disheartened, Hay never offered pardons to Burr’s other intimates.

A Drawn Battle

Despite two failed attempts to convict Burr, Jefferson still would not let his prosecutors retire from the field of battle. “We had supposed we possessed fixed laws to guard us equally against treason and oppression,” he wrote angrily, “but it now appears we have no law but the will of the judge.”

The government therefore assembled a new treason indictment that charged the former vice president with levying war against the United States when he had joined his adventurers on the Ohio River and then sailed all the way down the Mississippi. Chief Justice Marshall now needed to rule on whether probable cause existed for believing that Burr had committed that crime. Presiding over that preliminary issue without a jury, the judge’s attitude shifted dramatically. After five weeks of helping the defense tie the prosecution in knots, Marshall began to rule in favor the government.

Burr and his lawyers argued that another trial on treason charges, just after his acquittal on the same, amounted to double jeopardy. “This is the sixth trial which I have had to encounter,” Burr complained, “and it seems really desirous that I should know how many trials a man may undergo for the same thing.”