Having taken Dzhokhar Tsarnaev alive, prosecutors face a tangle of questions about what sort of evidence they develop and what they might present to a judge or jury down the road.

Among the decisions they face are when to inform the Boston bombing suspect of his rights to remain silent and to retain a lawyer—which will need to wait at least until Mr. Tsarnaev's physical condition improves—and whether to seek the death penalty.




Photos: Camaraderie After Boston Chaos


Timeline: Boston Bombings and the Search for Suspects

Map: Boston Area

Track locations of key incidents in the search for the suspects.

Timeline: Terror in the U.S.

Review other major plots of terrorism on American soil.

Mr. Tsarnaev, who has been hospitalized with various injuries since his capture Friday night, drifted in and out of consciousness during the weekend, a federal law-enforcement official said. Justice Department officials had hoped to charge the 19-year-old as soon as Sunday with crimes stemming from the Boston Marathon bombings, but the timing remains unclear.

Initially, some politicians and others suggested a military proceeding was more apt than one in federal court, but that was never seriously on the table because Mr. Tsarnaev is an American citizen accused of crimes in the U.S., with no evidence so far of a foreign nexus.

Another issue that continues to face the government: when to read Mr. Tsarnaev his "Miranda" warnings, informing him of his rights to counsel and to stay silent to avoid self-incrimination.

A federal law-enforcement official said shortly after Mr. Tsarnaev was taken into custody that authorities planned not to advise him of his rights at the outset, in the hope of questioning him about other potential explosive devices and other possible criminal conspiracies.

That approach might force the government to forgo using the fruits of its initial interrogation to prosecute Mr. Tsarnaev, though such information might be used for other purposes, such as developing or investigating leads. Or the government could try to persuade a judge that any confession by Mr. Tsarnaev resulting from such an interrogation could be used as evidence against him under the "public safety" exception to the Miranda rule.

That said, given the significant evidence that seems to be available already, including eyewitness accounts and video footage, a confession might not be necessary to win a conviction, said Michael Mukasey, a former federal judge and U.S. Attorney General under President George W. Bush.

"Giving up your ability to use a confession in this case is like giving up ice in winter," he said.

The prosecution will begin in full if and when Mr. Tsarnaev regains consciousness and strength, legal experts said. After an initial complaint is filed, Mr. Tsarnaev and his lawyer—likely the federal defender's office in Boston—would be expected to enter a preliminary plea. Shortly after, there could be wrangling over whether to grant Mr. Tsarnaev bail, though given the circumstances it is unlikely he would be released, legal experts said.

Mr. Tsarnaev could also face state criminal charges.

In the case of a federal guilty plea or conviction, the central question surrounding the death penalty, according to legal experts, would be whether Mr. Tsarnaev and his lawyers could persuade prosecutors that he should be spared—perhaps by extensively cooperating or by demonstrating that he deserved leniency.

"Was he mentally ill? Was he just blindly following his brother? Was his childhood particularly traumatic?" asked David Raskin, a former federal prosecutor in New York who handled several terrorism cases. "These questions don't go to guilt or innocence, but could be central to what ultimately happens here."

—Evan Perez, Alan Zibel and Jacob Gershman contributed to this article.

Write to Ashby Jones at ashby.jones@wsj.com