pile of bodies, the worst thing i think i've ever seen in my life. >> this morning, fierce resolve solve the crime and bring a killer to justice. >> make no mistake, we will get to the bottom of this and we we will find out who did this. >> it is tuesday, april 16th. >> announcer: from abc news, this is "world news now" with john muller and diana perez. and good morning. it was a day that was supposed to be a celebration with one of the nation's longest running sporting events at its core. >> the boston marathon always getting plenty of attention, unfortunately, this year it's for all the wrong reasons. [ explosion ] >> that was the sound that runners, fans and those providing support near the marathon's finish line heard yesterday when the explosions went off. one witness called the aftermath