NEW YORK (AP) — The Boston Marathon bombers were headed for New York’s Times Square to blow up the rest of their explosives, authorities said Thursday, in what they portrayed as a chilling, spur-of-the-moment scheme that fell apart when the brothers realized the car they had hijacked was low on gas.

New York Police Commissioner Raymond Kelly said Dzhokhar Tsarnaev told interrogators from his hospital bed that he and his older brother decided on the spot last Thursday night to drive to New York and launch an attack. In their stolen SUV they had five pipe bombs and a pressure-cooker explosive like the ones that blew up at the marathon, Kelly said.

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.

“We don’t know if we would have been able to stop the terrorists had they arrived here from Boston,” the mayor said. “We’re just thankful that we didn’t have to find out that answer.”

Dzhokhar was interrogated in his hospital room Sunday and Monday over a period of 16 hours without being read his rights to remain silent and have an attorney present. He immediately stopped talking after a magistrate judge and a representative from the U.S. Attorney’s office entered the room and gave him his Miranda warning, according to a U.S. law enforcement official and others briefed on the interrogation.