* Authorities learned of alleged plan from surviving suspect
* Father in Russia says he wants to visit United States
* "Broken" national security system - Republican senator
The two brothers suspected of carrying out last week's deadly Boston Marathon bombing decided, after the FBI released photos of them, to drive to Manhattan and detonate more explosives in Times Square, New York City officials said on Thursday.
Their plan unraveled when they realized a Mercedes sport utility vehicle they had hijacked on April 18, three days after the Boston bombing, did not have enough gasoline for the journey, said New York Police Commissioner Ray Kelly.
New York has been on heightened alert since the Sept. 11, plane hijackings in 2001 destroyed the World Trade Center and officials said the plan by the Boston bombing suspects, ethnic Chechens Tamerlan and Dzhokhar Tsarnaev, showed America's most populous city remained a magnet for attackers.
Manhattan's Times Square was the target of an attempted car bombing by a Pakistan-born U.S. citizen in May 2010.
In the sharpest criticism of President Barack Obama's security policies since the blasts, a Republican senator said the Boston bombing, which killed three people and wounded 264, illustrated a "broken" national security system.
This week, lawmakers demanded answers about what the U.S. government knew about the suspects before the bombing, especially Tamerlan Tsarnaev, 26, who Russia had asked the FBI to question in 2011 over concerns he may have been a radical Islamist. He died on Friday in a shootout with police.
The surviving brother, 19-year-old Dzhokhar Tsarnaev, is recovering from wounds in a Boston hospital since he was captured on Friday night and told investigators of the alleged Times Square plan.
"Questioning of Dzhokhar revealed that he and his brother decided spontaneously on Times Square as a target," Kelly told a news conference with New York 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 refuel, the driver of the vehicle escaped, Kelly said. The driver alerted authorities and set off a late-night chase and shootout in suburban Watertown, where police say the suspects threw improvised explosives at officers. Hours earlier, the brothers had shot and killed a Massachusetts Institute of Technology campus police officer in Cambridge, authorities said.
Earlier on April 18, the FBI released photos and video of the at the scene of the Boston bombing.
One Republican congressman said investigators have identified "persons of interest" in the United States to whom they would like to speak, some of them because of calls made from Tamerlan Tsarnaev's cell phone.
"There are also persons of interest here that we would like to more fully understand," said Mike Rogers, the chairman of the House of Representatives Intelligence Committee. "Their relationship and what role, if any, they may have played in that whole radicalization process. They are just still persons of interest, so they are not named."
Rogers also said investigators want to learn more about Tamerlan Tsarnaev's 2012 visit to Russia.
PARENTS SAY SONS INNOCENT
Dzhokhar Tsarnaev was formally charged on Monday in the hospital with crimes that could carry the death penalty.
His lawyer, Miriam Conrad, declined to comment 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 Tsarnaev might be moved from the Beth Israel Deaconess Medical Center.
The brothers' father 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 him while apprehending him.
Tsarnaeva does not plan to accompany her former husband on his trip. One factor that may have influenced her decision is an outstanding arrest warrant for her 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.
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 this 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."
Nonetheless, Republican Senator Lindsey Graham 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 told reporters, 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.