* Authorities learned of alleged plan from surviving suspect
* Father in Russia says he wants to visit United States
* "Broken" national security system - Republican senator (Adds comments from Massachusetts governor, background)
By Edith Honan and Mark Hosenball
NEW YORK/WASHINGTON, April 25 The two men suspected of carrying out last week's deadly Boston Marathon bombing decided after authorities identified them to drive to Manhattan and set off additional explosives in Times Square, New York City officials said on Thursday.
Their plan unraveled only when they realized that a Mercedes sport utility vehicle they had hijacked on April 18, three days after the bombing, did not have enough gasoline for the journey, Police Commissioner Ray Kelly said.
New York has been on heightened alert since the Sept. 11, 2001, hijacked plane attacks that destroyed the World Trade Center. Officials said the Tsarnaev brothers' alleged impromptu plan showed America's most populous city remained a magnet for those who want to strike at the United States.
Times Square was the target of an attempted car bombing in May 2010. A Pakistan-born U.S. citizen was arrested, admitted to the plot and is serving a life prison term.
In the sharpest criticism of President Barack Obama's security policies since the blasts, a Senate Republican said the Boston bombing attack - which killed three people and injured 264 others, illustrated a "broken" national security system.
Kelly said investigators learned of the alleged Times Square plan while questioning the surviving suspect, 19-year-old Dzhokhar Tsarnaev, in his hospital bed in Boston. Tsarnaev has been recovering from his wounds there since being captured on Friday night after an all-day manhunt that shut down much of Boston.
"Questioning of Dzhokhar revealed that he and his brother decided spontaneously on Times Square as a target," Kelly told a news conference with Mayor Michael Bloomberg. "They would drive to Times Square that same night.
"That plan, however, fell apart when they realized that the vehicle that they hijacked was low on gas and ordered the driver to stop at a nearby gas station," Kelly said.
At the time, the men still had six explosive devices, including a pressure-cooker bomb of the type used at the marathon and six pipe bombs, he said.
When they stopped to fill up the vehicle, the driver of the car escaped, Kelly said. The driver alerted authorities and sparked a late-night car chase across the university town of Cambridge, where police said the brothers shot and killed a Massachusetts Institute of Technology campus police officer.
Earlier on April 18, the FBI identified the ethnic Chechen brothers as suspects in the Boston bombing, releasing pictures and video of them at the scene.
The chase ended in an extended gun battle in suburban Watertown in which authorities said the suspects threw improvised explosives at police. The older suspect, 26-year-old Tamerlan Tsarnaev, was shot and died of his wounds.
Dzhokhar Tsarnaev was captured the next night in Watertown, hiding in a boat parked in the backyard of a house. He was formally charged on Monday in the hospital with crimes that could carry the death penalty.
His lawyer, Miriam Conrad, declined to comment on Thursday on whether her client was still talking with investigators.
The U.S. Marshals Service, which is responsible for holding and transporting suspects outside of prison, declined to comment on whether or when he might be moved from the Beth Israel Deaconess Medical Center.
PARENTS SAY SONS INNOCENT
The father of the brothers said he planned to travel to the United States from Russia to bury his older son, Tamerlan Tsarnaev.
"I am going to the United States. I want to say that I am going there to see my son, to bury the older one. I don't have any bad intentions. I don't plan to blow up anything," Anzor Tsarnaev told reporters in Makhachkala, the capital of Russia's Dagestan region.
Massachusetts Governor Deval Patrick said investigators might be interested in speaking to the parents.
"There are a lot of questions unanswered about the whys and the hows, and anybody who may be able to shed some light on that is of interest to law enforcement," Patrick said.
Anzor Tsarnaev's former wife, Zubeidat Tsarnaeva, angrily denied that her son had any role in the attack and criticized police for shooting her 26-year-old son while apprehending him.
Tsarnaeva does not plan to accompany her former husband on his trip. One factor that may have influenced Zubeidat Tsarnaeva's decision not to travel with her former husband is an outstanding arrest warrant in Massachusetts.
A warrant for Zubeidat Tsarnaeva's arrest was issued on Oct. 25 after she failed to make a court appearance on shoplifting-related charges, according to Natick District Court Clerk Brian Kearney.
Tsarnaeva was arrested in June at a department store on suspicion of shoplifting $1,624 worth of women's dresses, according to the Natick Police Department.
In Washington, the focus remained on intelligence leading up to the Boston Marathon bombing. Tamerlan Tsarnaev had been on a federal database of potential terrorism suspects and the United States had twice been warned about him by Russian authorities. Congressional testimony earlier in the week focused on whether the FBI made mistakes in tracking him.
"We're in the post-event witch-hunt phase, which is predictable," said James Clapper, director of national intelligence, at a conference in Crystal City, Virginia. "I think it would be a real good idea to not hyperventilate for a while now until we actually get all the facts."
Republican Senator Lindsey Graham told CNN he blamed the administration for failing to stop the attack.
"I just know the system is broken. The ultimate blame I think is with the administration," the South Carolina senator said, linking the bombings with last year's killing of a U.S. diplomat during an attack on a diplomatic compound in Benghazi, Libya.
"Between Benghazi and Boston, to me we're going backwards, not forward, in terms of national security," Graham said. (Additional reporting by Tim McLaughlin, Svea Herbst-Bayliss, Aaron Pressman, Ross Kerber in Boston, Deborah Charles in Crystal City, Virginia, Alissa de Carbonnel in Makhachkala, Russia, and Atossa Araxia Abrahamian in New York; Writing by Scott Malone; Editing by Paul Thomasch, Grant McCool and Peter Cooney)