Police Commissioner William B. Evans said he cannot shake the image of a lifeless Janmarcos Pena, the 9-year-old Mattapan boy who was allegedly killed by his older brother.

Evans had been on the Mattapan street that morning last month, as the curly haired boy was carried out of his home on a stretcher and then to the morgue. Janmarcos’s 14-year-old brother, who police said had been playing with a gun, has been charged in the death.

On Monday, Evans stood as the city’s top police officer and as a parent at a park near Dorchester’s Codman Square neighborhood to announce the “Your Piece for Peace” gun buyback program, the city’s latest initiative aimed at reducing violence by firearms. Speaking at a news conference, he appealed to parents, girlfriends, or relatives to help police save a young child who might be in peril.

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“I happen to be there when they were wheeling him out. I went to the kid’s wake,’’ Evans said of Janmarcos. That should be “a wakeup call to people to get into their kids’ closets, get into their daughter’s pocketbooks, and help us out and get those guns into our custody so that we don’t have young kids dead on the street.”

Despite research suggesting gun buybacks do little to stops shootings, Evans and Mayor Martin J. Walsh pressed ahead with the initiative Monday, saying it was part of a comprehensive strategy to curb gun violence. Already, they said, police have seized 136 guns this year.

Walsh said the city also will host a regional gun trafficking summit later this spring, where officials will discuss preventing illegal guns from crossing state lines. And he is seeking more funding for summer jobs for youths, to keep them occupied and out of trouble.

Among its goals, the buyback program, conceived with input from churches, neighborhood workers, and tenants groups, will raise awareness and mobilize residents around addressing the problem, the mayor said.

“Removing guns from our neighborhoods is at the heart of our violence prevention,’’ Walsh said at the news conference. “And that is what this program will do. Every gun turned in is a potential to save a life.”

Under a bright, cold March sky, Evans and Walsh stood on Dr. Loesch Family Park with clergy members who have buried slain teenagers, with community champions working to keep the peace, and with mothers who have lost their sons to gun violence.

Tina Chery, who runs the Louis D. Brown Peace Institute, said people who have lost loved ones to prison or the grove should join the effort.

“Within our community we are losing at both ends,’’ said Chery, whose institute is named for her 15-year-old son, who was cut down by a stray bullet. “We ... have the power to turn those guns in. And it is going to take courage.“

Authorities urged not only participation, but also donations to keep the program going. The buyback program now has a $125,000 budget, with money from the Boston Police Athletic League, the City of Boston Credit Union, and Boston Police Runners Club, the mayor said, promising corporate funding.

In 2013, Boston police responded to 260 shootings and confiscated 667 guns, many of them small 9mm weapons used in street crimes, Evans said.

Just last week, police responding to panicked female caller found two loaded shotguns—a 20-gauge Mossberg and a 12-gauge Remington—leaning against a closet wall in a bedroom in a Mattapan home.

So far this year, there have been 15 homicides, including 11 killed by gunfire, police said.

The “Piece for Peace” program will be held from noon-7 p.m. weekdays. Residents can anonymously turn in an active gun—guns typically used to commit crimes—at about two dozen drop-off sites and receive a $200 Visa gift card, no questions asked. People who want to turn in firearms privately can call (888) GUNTIPS between 8 a.m. to 11 p.m.

The program requires that the weapons are delivered unloaded. They must be in clear plastic bags and inside another container such as a gym bag or backpack. Ammunition must be in a separate bag; and guns must be transported in the trunk of a vehicle if they being driven to a drop-off site.

Residents won’t be prosecuted for unlawful possession of a gun they turn in, but each weapon will be tested to determine whether it was used in a crime. If the test comes back positive, an investigation will be launched, authorities said

Evans said police are being selective in the firearms they accept in the program. The commissioner said police will not accept stockpiles of guns from dealers looking to discard old firearms, or weapons that have been in someone’s basement collecting dust. Police will take rifles and shotguns, but will not give a financial incentives for those weapons.

As of 7 p.m. on Monday, 25 guns had been turned in, according to David Estrada, a police spokesman. They included some 9mm and .380-caliber handguns, firearms commonly found tucked in a suspect’s waistband, or discarded on a side street after a police chase, Evans said.

The last buyback program eight years ago netted some 1,000 guns.