keith morrison (voiceover): what happened to matt podolak? who knew? parently not the coroner, who had still not issued any official report. and then finally, three months after matt's death, mark got a call from his mother. come to a family meeting, she told him. she refused to tell him what would be said there. because i knew he would be very, very upset. keith morrison (voiceover): the news was too bizarre, too shocking, to share over the phone. coming up. the whole family was there, and i kind of lost it. keith morrison (voiceover): the coroner's report makes it clear matt's death wasn't just strange. it was also highly suspicious. we were all thinking it was kidney failure. we were not expecting that. it was my mission to find an answer for this. keith morrison (voiceover): when "dateline" continues. ooo! our car's value went up! maybe we should track all our cars' value on carvana? we need more trackers! oh! i'm getting a value update! do you see which one is going off? how's it trackin'? some dips, some rises. now what? "hold?" sold. track your c

keith morrison (voiceover): and there was still a podolak playing amateur hockey here in cleveland. matt loved the game. mark took it up in his memory. and since matt couldn't be here to play, said mark, he'd play for him. hello, i'm craig melvin, and this is "dateline." katherine walton: it was just chaos. hello, i'm craig melvin, and this is "dateline." craig melvin: a day at the mall descends into mayhem as armed men turn shoppers into prey. lots of screaming, lots of gunfire. they had a demeanor like they owned the place. craig melvin: panicked moms protecting their kids. i just kept telling them to be quiet like a mouse. my goodness, he's going to cry. this is it. craig melvin: kids forced to protect one another. you grabbed your brother. yeah, and just ran. craig melvin: and from out of the blue, a hero. i just called to her to run towards me and she starts running. craig melvin: could he rescue the very smallest of victims? when portia got up and ran, did you have a moment where you thought, oh my god. hello and welcome to dateline. newtown, orlando, las vegas. it seems like mass