NEW YORK - Armed with a pressure-cooker explosive and five pipe bombs, the suspects in the Boston Marathon bombing made a spur-of-the-moment decision last week to give the Big Apple a taste of their mayhem, New York officials say.

The potentially deadly scheme fell apart when the brothers realized the car they had hijacked was low on gas.

"We don't know if we would have been able to stop the terrorists had they arrived here from Boston," Mayor Michael Bloomberg said Thursday. "We're just thankful that we didn't have to find out that answer."

New York Police Commissioner Raymond Kelly said Dzhokhar Tsarnaev told interrogators at his hospital bed that he and his older brother spontaneously decided the night of April 18 to drive to New York and launch an attack.

But when the Tsarnaev brothers stopped at a gas station on the outskirts of Boston, the carjacking victim they were holding hostage escaped and called police, Kelly said. Later that night, police intercepted the brothers in a blazing gunbattle that left 26-year-old Tamerlan Tsarnaev dead. Dzhokhar, 19, was discovered hiding in a boat in a suburban back yard the next day. He was wounded.

It is questionable whether the Tsarnaevs could have successfully made the 200-mile trip to New York since they had become two of the most-wanted men in the world since the April 15 explosions that killed three people and injured more than 260. Their faces had been splashed all over the Internet and TV in surveillance-camera images released by the FBI. Yet the news that the city may have narrowly escaped another terrorist attack still made New Yorkers shudder.

Dzhokhar Tsarnaev is charged with carrying out the Boston Marathon bombing April 15 that killed three people and wounded more than 260. He has been moved from a Boston hospital to a federal medical center about 40 miles west of the city, the U.S. Marshals Service said Friday.

Authorities say Tsarnaev could get the death penalty. Christina DiIorio-Sterling, a spokeswoman for U.S. Attorney Carmen Ortiz in Boston, would not comment on whether authorities plan to add charges based on the alleged plot to attack New York.

Meanwhile in Massachusetts, the Middlesex County district attorney's office said it is building a murder case against Tsarnaev for the death of MIT police officer Sean Collier three days after the bombings.

As authorities began disclosing the suspects' plans and motives, the hospital-room questioning of Tsarnaev is generating concern about whether he should have been interrogated without first being told of his constitutional rights to stay silent and have a lawyer present — and, conversely, whether federal agents actually should have had more time with him before he was read his rights.

Tsarnaev faced 16 hours of questioning before he was advised of his Miranda rights, and investigators say he told them of his role in the two bombings near the Boston Marathon finish line. He explained that he and his brother were angry about the U.S. wars in Afghanistan and Iraq and the killing of Muslims there, according to two U.S. officials who spoke on condition of anonymity because they weren't authorized to discuss the case with reporters.

Tsarnaev also described their plan to drive to New York and set off the remaining explosives there.

In Boston, federal agents invoked an exception to the Miranda warnings that allows for questioning when public safety may be threatened. But they knew their time with Tsarnaev in the absence of a lawyer would be limited.

On Sunday, prosecutors filed a criminal complaint charging Tsarnaev with a role in the bombings. That action led directly to an improvised court hearing in the hospital the following morning at which U.S. Magistrate Judge Marianne Bowler told Tsarnaev he did not have to answer questions and could have a lawyer. He then stopped talking.

Civil liberties advocates have said a suspect should rarely be questioned without a lawyer and without being told he doesn't have to respond.

"Miranda rights are an incredibly important civil liberties safeguard," said Hina Shamsi of the American Civil Liberties Union. "The public safety exception must be read narrowly, as it has been by the courts."

But California Democratic Rep. Adam Schiff, a former federal prosecutor, said he has questions about how the court proceeding came about.

"I would have thought the public safety exception would have allowed more time for the questioning of the suspect prior to the arraignment and/or advising of rights," Schiff said.

Based on the younger man's interrogation and other evidence, authorities have said it appears so far that the brothers were radicalized via Islamic jihadi material on the Internet instead of any direct contact with terrorist organizations, but they warned it is still not certain.

The brothers are ethnic Chechens from Russia who came to the United States about a decade ago with their parents. The family was granted asylum.