BOSTON — "Gotcha!"
That one-word message on a a jumbo electronic expressway billboard Saturday expressed the relief and the gratitude of a city under siege since the Boston Marathon bombings but which saw that fear end with the death of one suspect and the capture of the other Friday.
Now, authorities said, their investigation will focus on why brothers Dzhokhar and Tamerlan Tsarnaev, natives of Russia, planted two homemade bombs near the race course finish line that killed three spectators and maimed more than 170.
U.S. Attorney Carmen Ortiz said the prosecution's "journey begins" and won't end until it is determined if the Tsarnaev brothers were part of a larger terrorist organization or acted on their own.
The effort to find the motive behind the bombings was made easier Friday night when police captured a badly wounded Dzhokhar Tsarnaev, 19, in a 20-foot, shrink-wrapped boat drydocked in a residential backyard in the suburb of Watertown on Boston's western edge.
His brother, Tamerlan Tsarnaev, 26, was killed early Friday morning in a shootout with police that Dzhokhar managed to escape from despite what police said was the exchange of 200 rounds of ammunition.
President Obama praised the army of law enforcement officials that had pursued leads in the marathon bombings, and ended the week-long dread that had paralyzed Boston in the wake of the bombings at an iconic event. He said the federal government would "deploy all necessary resources" to determine why the marathon bombings occurred.
"We will investigate any associations that these terrorists may have had," he said. "And we'll continue to do whatever we have to do to keep our people safe."
The captured suspect holds the key to the next phase of the investigation. He is under sedation at Beth Israel Deaconess Hospital in Boston after surgery for bullet wounds in his neck, legs and torso sustained in two gunfights with police. His hospital room was under heavy police guard.
The first of the police shootouts occurred about 1 a.m. Friday in Watertown, touched off by reports of a campus police officer being shot to death on the MIT campus in neighboring Cambridge. The Tsarnaev brothers, meanwhile, had carjacked a black Mercedes SUV in Cambridge, and were soon pursued by police, exchanging gunshots with police and throwing homemade pipe bombs at them. The chase ended in Waterford, where the older brother was felled in a hail of bullets. Authorities said he was wearing a small bomb strapped to his chest. His younger brother, who was also hit by gunfire, sped from the scene in the SUV, then abandoned it and fled on foot.
The second police gunfight occurred 18 hours later when police were discovered the fugitive suspect hiding in a 20-foot boat. Several shots were exchanged before police dragged the wounded suspect from the boat's cockpit, handcuffed him and took him to the hospital for medical treatment.
Authorities said once the suspect is out of medical danger, he will be interrogated by a special federal government interrogation team made up of FBI, CIA and Defense Department officials. He will not have a lawyer present because he is considered a national security risk.
U.S. Attorney Ortiz said the special interrogatin team will seek to determine if the brothers had help in plotting the marathon bombings and where they got the materials for the pressure cooker bombs they used.
"We owe it to the victims and the American public to get to the bottom of this terrorism," she said.