Mayor Martin Walsh, right, was on hand at the White House last week to listen to President Obama’s remarks about executive action on gun control measures. AP Photo/Jacquelyn MartinI traveled to Washington D.C. last week and stood with President Obama as he took measures to make our communities safer. Requiring all gun purchases to include a background check is a common sense, simple step that will make it harder for criminals and those who intend to commit crimes to access firearms.

Some 1.5 million Americans have been killed by gunfire on US soil since 1968. Mass shootings rightfully command our attention; we average 33 gun deaths daily. That amounts to a collective mass shooting every single day. America has a problem with gun violence.

Boston is one of America’s safest large cities, and our 33 gun homicides last year made for a historically low number.

Yet taken together, they would rate with the deadliest mass shootings in US history. And because these deaths are concentrated in a small number of communities, their traumatic impact is not so different from that of a mass shooting.

Mayors and police chiefs see the fallout up close. We visit crime scenes and sit with families. We see the trauma, the impact on public health, on education, on job growth, on community pride and neighborhood well being.

The inability of Congress to pass even the most common-sense measures, likebackground checks, is discouraging. But we can’t allow ourselves to become apathetic. We have to ask why and how this is happening, and what we can do to stop it.

In Boston, we have gone all-in on police-community relations. We’ve created a Social Justice Task Force made up of clergy and community leaders, held Peace Walks in affected neighborhoods, and made our gun buyback a tool of community engagement. We’ve brought services to the highest-risk young people from the earliest age we can identify them. These actions have made a difference and we have had a steady stream of interest in our policies from other cities and from the US attorney general’s office.

Ultimately, we have an issue of access to guns that originates far beyond the local community. Our police officers have taken 1,061 guns off the streets in 2014, and 785 guns in 2015. We’re looking to make even more progress in 2016, but the guns keep coming. With nearly 70 percent of Boston’s crime guns coming from outside Massachusetts, we know that this is not just a local issue, or an inner-city issue. Guns move across city and state lines and all too easily from legal ownership to criminal possession.

We have to reach beyond city limits to find a solution. If we had a contaminated food supply, we would treat the sick and we would urge safety measures, but we would go much further. We would find the source of the contamination and clean it up without delay, even if that took us out of state. That’s how we should treat gun violence as well. We do all we can to make our communities safe, but we have to move up the chain to find the source of the problem.

We have partnered with the Bloomberg Foundation’s Everytown for Gun Safety, and with the Rappaport Institute at Harvard, to research the origins of crime guns in Boston. It showed that two-thirds of our crime guns come from states with weak gun laws. We have convened regional gun trafficking summits to forge data-sharing agreements with neighboring states, but we also found that nearly one-third of the crime guns recovered in Boston were first sold by federally licensed gun dealers right here in Massachusetts.

The vast majority of those guns were not held by the original buyer, nor had they been reported as sold, lost, or stolen.

These findings are troubling, but they open a window for action. The law that the Legislature passed last year requires prior approval and registration of private gun sales. As the state ramps up enforcement, we will be able to stop legally purchased guns from becoming crime guns.

Locally, we are starting the conversation. We have sent a letter to every licensed gun owner in the city of Boston explaining the new law, promoting the buyback program, and offering a free gun lock as well as safety advice.

One gun owner from Dorchester wrote back and said, “until your letter, we have been virtually excluded from the discussion of how to reduce violence.” We expect legal gun owners to be valuable partners moving forward.

Another challenge is holding retailers, distributors, and manufacturers accountable for safe practices. To do so, we have joined with the nonprofit Arms with Ethics to create the Boston Responsible Gun Vendor Initiative.

Local governments and law enforcement agencies are one of the industry’s biggest markets, spending more than a billion dollars each year on guns and ammunition. Moving forward, bidders for gun contracts with the Boston Police Department will be scored on the measures they take to prevent straw purchases and theft, and we will offer all vendors support and advice on adopting and documenting best safety practices.

In 2015 in the City of Boston, gun homicides were down considerably (an 13.5 percent decrease from 2014), but shootings were slightly up (an 18 percent increase from 2014 for non-fatal shootings). We should resist any temptation to see a non-fatal shooting as a minor event: children are growing up in our city believing that getting shot is a common occurrence. We must begin answering the tough questions, as well as asking them. We have the tools. We have the will. Let’s not wait any longer. Let’s make a difference together. Let’s show the nation a way out of this crisis.