Boston bombing: What investigators need to find out now

(CBS News) Amid the cheers of celebration and the sighs of relief all across Boston -- all across this country -- the investigation into the bombings and their perpetrators is moving ahead, as John Miller reports.

It was a week of images both frightening and inspiring: The chaos of a terrorist attack -- and the heroism of the response.

In eerie videos from security cameras we saw brothers Tamerlan and Dzhokhar Tsarnaev allegedly on the way to place the bombs . . . then, the gripping 28-hour manhunt. There was an ambush that left a young police officer dead, and a gun battle that left a transit police officer badly wounded, and ended the life of Tamerlan Tsarnaev.

Dzhokhar Tsarnaev, his younger brother, was at last spotted hiding inside a boat as the dragnet closed around him.

His FBI wanted poster -- now marked "captured" -- is the image that puts to a close the first chapter in the story of the Boston Marathon bombings.

And so the next chapter opens with nothing but questions -- questions posed by the president himself:

"Why did young men who grew up and studied here, as part of our communities and our country, resort to such violence?" Mr. Obama said. "How did they plan and carry out these attacks, and did they receive any help? The families of those killed so senselessly deserve answers."

Answers that the full force of U.S. law enforcement and intelligence agencies are racing to learn.

Was there foreign help or training? Older brother Tamerlan spent six months overseas last year. He went to Dagestan and Chechnya -- areas where Islamic extremists and violent Chechen separatists are known to operate.

Six months was "long enough to have done a lot of things," said Robert McFadden, a former agent in the NCIS (the Naval Criminal Investigative Service). His 30-plus years' experience in counter-terrorism includes work on the al Qaeda bombing of the USS Cole in 2000.

"If you're motivated, have the connections, there's plenty of time there to be initiated into a group, receive training -- potentially a lot of training."

McFadden believes the number-one priority of investigators is to be sure there are no accomplices still at large.

"Are there other events coming?" he said. "What other events are planned?" Investigators must do everything possible, he said, "to rule out that there could be other terrorist acts in place and so do everything possible to disrupt that."

As for the surviving brother, Dzhokhar Tsarnaev, a gunshot wound to his neck currently prevents him from speaking. Investigators believe it may have been self-inflicted -- a possible suicide attempt.

Needless to say, many want to hear what he has to say, including Massachusetts Governor Deval Patrick.

"All of the law enforcement professionals are hoping, for a host of reasons, that the suspect survives because we have a million questions," Patrick said.

In a controversial move, the Justice Department plans to begin questioning Tsarnaev before reading him his Miranda rights, saying investigators need immediate information on any attacks that may be in the works.

The pressure is on to learn exactly where this trail of bloodshed began.