. >> reporter: david witt stands on the corner in baltimore where for one day violence raged, and for a week, huge mostly peaceful protests took over the streets, capturing the world's attention. >> if i have to die to get the police to do the right thing, i'm dead you know. i will willingly give my life up for my kids. >> it may seem like he's protecting his own neighborhood but he's not. >> people will be reminded number one, who the enemy is. >> is that police? >> exactly. they are the number one enemy. >> this is where we first meet him, on the streets of ferguson. whitt lives just steps from the spot where michael brown was shot and killed by police officer darren wilson. >> why did you come from ferguson? >> the first reason i came because one of the cop watchers on the ground, got arrested. >> he started a chapter of cop watch in ferppingz, raising money to give cameras to police. since then he's traveled to north charleston, south carolina, oakland, and now baltimore. >> would you consider yourself a professional what? cop watcher? what would you consider yourself? >> i think

>> reporter: interestingly enough, david witt? >> yes, ma'am. >> i just recognized david as he was having a conversation, if you will, with the police officers here. he's come all the way from ferguson. i recognize him from ferguson, missouri. can i ask you, are you going to obey this curfew that is happening right now, are you going home? >> well, honestly right now, we got our people with our press pass, so we good, we going to stay out here, with the peoples, we gonna document what happens. you see people that's hout here, they getting ready to move in, so this is what we do. so we able to stay out here past the curfew. >> you started this, you started getting into this because of what happened to michael brown, right? >> absolutely. now what we doing is making sure that other communities are equipped with the same knowledge that we began to use out in ferguson. and the guy that videotaped gray being abused, he's actually decided willingly, we contacted him, he's like, we want to do this watch thing so we got him on camera. he o

david lettermannen bow out from late night? bow out from late night?out from late night? >> welcome to "weekends with alex witt."h the new developments in the murder mystery in vice president biden's d.c. neighborhood. police released surveillance video which shows a person of interest in the case. a fire that tore through this multimillion dollar home this week was an act of arson that led to the discovery of four bodies inside the home. nbc's kristinton welker has been following the story. what more can you tell us about the investigation? >> it is a tragedy. miss say the man in the video you just showed is a person of interest and they're asking for the public's help in finding him. police released that video last night. in it, you see that man dressed in dark clothing. he's wearing a hoodie and moving very quickly behind a building. according to authorities he may have been operating a blue porsha that was initially seen parked outside of that house that burned down. car was later found toed and ten miles away from the house. police are calling this an arson and homicide investigation. they say on thursday a