TODAY

TODAY   |  April 17, 2013

FBI to follow up on thousands of bombing tips

As investigators continue to piece together the events of the Boston Marathon bombing, combing every inch of the finish line, they are also following up on tips from over 2000 eye witnesses. NBC’s Lester Holt reports.

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>> up, the fbi right now poring over evidence, photos and videos of the boston marathon bombing and for the first time we are seeing parts of an explosive device that was used, a twisted piece of metal from what is believed to be a pressure cooker .

>> investigators are also examining these photos sent to our nbc station in boston , whdh. you can see a bag lying next to a mailbox along the race route and the aftermath and it appears one of the explosions took place right where that bag was sitting. officials are trying to determine if that bag contained the second bomb. as for a suspect and motive, fbi says that part of the investigation remains wide open .

>>> a number of vigils were held last night for the three people who died including a huge gathering in the hometown of 8-year-old martin richard. natalie morales is in boston with that part of the story. but we begin with nbc 's lester holt and where this investigation stands this morning. good morning to you.

>> reporter: savannah, good morning. the investigation made some remarkable progress on tuesday as investigators discovered parts of the bomb itself, learned more about its construction, lals laced with pellets and nails to inflict maximum damage. recovering the bombs is one piece of a very complex puzzle. investigators are now combing every inch of the boston marathon finish line looking for clues linked to monday's terrorist attack including analyzing one of the bombs it self. this morning, we are getting our first look at the mangled remains of an explosive device collected at the scene. these photos were released by the fbi .

>> among items partially recovered are pieces of black nylon which could be from a backpack and what appear to be fragments of bebes and nails, possibly contained in a pressure cooker device.

>> reporter: this as authorities follow up on more than 2,000 tips from eyewitnesses, photos like these obtained by our nbc affiliate whdh indicate nylon bags might have been placed in trash bags near the marathon route. we do not know if the bag in question is relevant but it is one of many possible leads investigators are pursuing. ben thorndike works in a building that overlooks the finish line . he took these still photos after the first explosion. the chaos is clear, this man with clothes torn by the blast runs away.

>> even though it wasn't video in some ways it was better because you could see things unfold.

>> tuesday night a vigil for 8-year-old victim martin richard was held in his hometown of dorchester, massachusetts.

>> i think of my own kids. i just can't imagine the pain that they're going through.

>> reporter: a moment of silence was also observed at yankee stadium during last night's game, to remember the young boy and two others killed, abunnamed chinese graduate student and krystle marie campbell a 29-year-old from medford, massachusetts.

>> we're heartbroken at the death of our krystle marie. she was a wonderful person. everybody that knew her loved her.

>> reporter: raw emotion from families and loved ones still struggling to grasp the unthinkable. investigators are saying somebody knows who did this. they've made a broad appeal to the public, asking people to come forward if they know of someone who was looking for ingredients for a bomb, maybe they heard someone testing, heard an explosion, anyone who has information they're asking to come forward, they've had as we note more than 2,000 tips and matt, the president will be here in boston on thursday to speak at a memorial service and help this community as it continues to heal.

>> lester holt in boston this morning, lester thank you very