BAL­TIMORE—”This is a bad neigh­bor­hood,” the cab­driver tells me as we pull up to an ugly, beige, low-rise build­ing in the pre­dom­in­antly Afric­an-Amer­ic­an neigh­bor­hood of Lower Park Heights. The dappled sun­light on the tree-lined street be­lies the fact that this area has one of highest per cap­ita crime rates in Bal­timore.

There are bars on the steel door en­trance to the build­ing and a keypad lock. It looks like a deser­ted pris­on. I’m re­lieved when the door opens be­fore I exit the cab and a middle-aged guy with an ID tag emerges talk­ing on his phone. He waves to me, and I real­ize he is Mi­chael Schwartzberg, the pub­lic in­form­a­tion of­ficer for Bal­timore’s Health De­part­ment.

Schwartzberg has set up in­ter­views for me with con­victed crim­in­als, but we aren’t meet­ing at a pris­on. We’re meet­ing in the headquar­ters of Park Heights Safe Streets. The ex-cons are two of their trus­ted staff mem­bers.

Pro­sa­ic­ally typecast, they are both wear­ing bright-or­ange shirts.

One staffer, Greg Marsh­burn, was in and out of pris­on over a peri­od of 17 years for a num­ber of crimes, in­clud­ing at­temp­ted murder and rob­bery. He has been shot four times and stabbed at least 20. He was asked to be a wit­ness after one of the shoot­ings but re­fused to identi­fy his at­tack­ers. “I let the guys go be­cause I was rob­bing them,” he ex­plains. “To me, that was my civic duty.”

Marsh­burn’s cur­rent job makes use of his old con­tacts and his street cred, which is bolstered by the at­temp­ted-murder charge and his un­will­ing­ness to rat out his as­sail­ants. He is a su­per­visor at Safe Streets, one of a small staff of black men who can­vass the neigh­bor­hood like beat cops.

But they are in no way po­lice. The Safe Streets men are un­armed and work among gun-tot­ing gangs without pro­tect­ive gear. They don’t care if you’re selling drugs or do­ing drugs. Their mes­sage is simple: Just don’t shoot any­body.

Safe Streets in Bal­timore is one of a half-dozen op­er­a­tions in in­ner cit­ies throughout the coun­try set up by Cure Vi­ol­ence, a non­profit foun­ded in 1995 by epi­demi­olo­gist Gary Slutkin that ap­plies the ten­ets of dis­ease erad­ic­a­tion to re­du­cing shoot­ings and hom­icides. The premise of Cure Vi­ol­ence is that vi­ol­ence clusters and spreads like an epi­dem­ic vir­us, and it can be stopped the same way an epi­dem­ic is stopped—by in­ter­ven­ing at the source, re­du­cing risk for those at highest risk, and chan­ging com­munity norms.

The geni­us of Cure Vi­ol­ence lies in its tar­geted, al­most clin­ic­al ap­proach to re­du­cing shoot­ings, as­saults, and hom­icides. The group sees in­cid­ents of vi­ol­ence much the same as cases of HIV, tuber­cu­los­is, or even Ebola are viewed. Vi­ol­ence spreads when people are in­fec­ted with it. It stops when those ex­posed to it stop in­fect­ing oth­ers.

Cure Vi­ol­ence aims its in­ter­ven­tions at the worst places. In Bal­timore, neigh­bor­hoods must fall with­in the top quart­ile of non­fatal shoot­ings and fire­arms hom­icides to qual­i­fy to be­come a Safe Streets site. Even in those des­ig­nated spots, pub­lic-health work­ers won’t at­tempt to make in­roads un­less a ser­vice or­gan­iz­a­tion with­in that com­munity steps up and agrees to host the Cure Vi­ol­ence pro­gram.

The mod­el de­pends on com­munity buy-in for its suc­cess, a factor that polit­ic­al sci­ent­ists say is the most im­port­ant com­pon­ent of any type of civic en­gage­ment. Cure Vi­ol­ence’s meth­ods are de­signed to turn vi­ol­ent neigh­bor­hoods in­side out by re­cruit­ing their own res­id­ents—in­clud­ing, at times, con­victed crim­in­als—to make the ini­tial turn­around ef­forts. The only auto­mat­ic dis­qual­i­fic­a­tion for em­ploy­ment with Cure Vi­ol­ence is a his­tory of do­mest­ic vi­ol­ence or child ab­use.

Marsh­burn and his col­leagues are “trus­ted in­siders” who know enough about their neigh­bor­hood to an­ti­cip­ate where vi­ol­ence might oc­cur and in­ter­vene. They spend each eight-hour shift walk­ing their as­signed streets to “find out what’s go­ing on.” If a guy on one corner has a beef with an­oth­er guy on an­oth­er corner, Marsh­burn and his co-work­ers fig­ure out who among them knows the two in­di­vidu­als the best. Who is most trus­ted? If none of them know the parties very well, they look for a trus­ted third party, of­ten a moth­er or a grand­moth­er. They talk to each per­son in­di­vidu­ally. They per­suade them to back off. They call back the next day.

“You twist it. You say, ‘You go­ing to shoot that guy be­cause he stole $130 of drugs? Christ­mas is around the corner. Who’s go­ing to be Santa?’ ” says Dante Barks­dale, the out­reach co­ordin­at­or for Safe Streets.

(Barks­dale, by the way, is the oth­er former con­vict present at my in­ter­view. He spent eight years in pris­on for deal­ing bad heroin. And if his name sounds fa­mil­i­ar, yes, he is the neph­ew of former drug king­pin Nath­an “Bod­ie” Barks­dale, an in­spir­a­tion for Avon Barks­dale, a char­ac­ter in the HBO series The Wire.)

“I go as far as say­ing, ‘Who’s go­ing to raise your kids?’ ” Marsh­burn adds.

Site dir­ect­or James Timpson of­fers up an­oth­er mo­tiv­a­tion dir­ec­ted spe­cific­ally at the deal­ers. “If you want to make the block too hot, ain’t nobody can make any money.” (Timpson grew up in the neigh­bor­hood, but he cred­its his un­usu­al jail-less past to his par­ents, who sent him to board­ing school when he was a teen­ager.)

It’s now clear why these guys aren’t cops. They are will­ing to look the oth­er way on drug deal­ing and oth­er petty crime as long the vi­ol­ence stays at bay. Trust in the neigh­bor­hood is the most im­port­ant job qual­i­fic­a­tion for these “vi­ol­ence in­ter­rupters.” The No. 1 rule on the street is, “Don’t be a rat,” Marsh­burn says. Guys who have been seen talk­ing to the po­lice, even if the con­text is un­known, are already viewed sus­pi­ciously and are not cap­able of form­ing the re­la­tion­ships ne­ces­sary to per­suade po­ten­tially vi­ol­ent people to hold off. If they were ever a wit­ness in a pro­sec­u­tion, for­get it.

Marsh­burn got his re­fer­ral to Safe Streets about a year ago from an­oth­er site dir­ect­or whom he met in jail. He had just fin­ished his most re­cent trip to re­hab for a heroin ad­dic­tion and called up his buddy. “He said, ‘Man, I been look­ing for you,’ ” Marsh­burn says. ” ‘I got an op­por­tun­ity.’ “

Marsh­burn wasn’t go­ing to say no to any­thing that meant clean money, no mat­ter how crazy it soun­ded. He star­ted at Safe Streets as a vo­lun­teer, walk­ing his as­signed blocks and mak­ing con­nec­tions. He was care­fully vet­ted by a team of health pro­fes­sion­als and neigh­bor­hood lead­ers to see if he had a good repu­ta­tion and was able to handle con­flict res­ol­u­tion. Could he talk an angry per­son bent on re­tali­ation down? Could he per­suade high-risk in­di­vidu­als to let Safe Streets staffers keep in reg­u­lar con­tact? Could he stay clean?

His jail buddy en­cour­aged him. Marsh­burn says, “I nev­er had a job be­fore. I don’t have a résumé. He said, ‘You are your résumé. “… You me­di­ated a situ­ation for me in pris­on.’ “

Marsh­burn knows the ex­act date he star­ted get­ting paid for his work: Nov. 26, 2013. It’s been a big year for him. He was pro­moted to su­per­visor. He ment­ors young­er people in his neigh­bor­hood and is study­ing to be an ad­dic­tion coun­selor. At one time, par­ents kept their kids away from him. Now they want him to hang out with their chil­dren. He is 45, with three grown chil­dren of his own and four grand­chil­dren, ages 2 to 5. And yet this is the first year he has had his own place to live. “I don’t even want nobody to come over to my house,” he ad­mits with a sheep­ish grin.

Marsh­burn and his col­leagues are the vac­cine that, in Slutkin’s vis­ion, will in­ocu­late troubled com­munit­ies to vi­ol­ent out­breaks. This year, Safe Streets has me­di­ated 685 con­flicts in Bal­timore, with 624 of them deemed “likely” or “very likely” to have res­ul­ted in a shoot­ing. But that didn’t hap­pen.

The pro­gram can’t pre­vent every act of vi­ol­ence. As I pack up to leave, the crew starts talk­ing about a re­cent ar­rest in which a moth­er called po­lice when she found her son “wrap­ping up a body in the base­ment.” They don’t of­fer more de­tail.

Barks­dale dis­ap­pears in­to the back of­fice to find out more, then bel­lows in a deep bass voice, “Oh, my God! I knew it! I know all three of them.” He stands in the door­way, re­mem­bers I’m there, and shuts the door, yelling a bit more be­fore emer­ging, calmer.

I ask him to drive me back to the train sta­tion. I couldn’t feel safer.