For years, advocates in the United States have been pushing for a fuller accounting of the legacy of Indigenous boarding schools.

Starting from around 1819 and continuing through the 1960s, generations of Indigenous children were separated from their families and sent to the institutions, run by government or missionary organisations.

An estimated 100,000 children were sent to the schools during that period, although the exact number remains unknown. There, they were forced to assimilate into white American culture, and many faced outright abuse.

But while the US government has taken steps to address that troubling legacy as violence at the schools has come into increased focus in recent years, Indigenous leaders have questioned whether enough is being done.

Last year, Washington released the results of a first-of-its-kind investigation into the boarding schools and their policies. The initial report arrived under the leadership of Interior Secretary Deb Haaland, the first Native American woman to occupy the role.

The investigation found that the institutions became breeding grounds for “rampant physical, sexual and emotional abuse; disease; malnourishment; [and] overcrowding”, as they served a larger policy of seizing land from Indigenous people and erasing their culture. A second report from the probe is expected.

But advocates warn the 408 federally funded institutions identified in the report do not capture the full scope of the boarding schools.

In late August, the National Native American Boarding School Healing Coalition (NABS), an independent organisation, released a list that tallied a total of 523 boarding schools, including 105 with no known federal ties.

Now, a federal bill would create an independent truth and healing commission to investigate the ongoing effects of the boarding school system.

Under the proposed legislation, a 10-person panel would wield subpoena power, the legal authority to compel records and testimony. Proponents say that power is essential for accountability, as Indigenous communities continue to contend with the inter-generational harms of the boarding schools.

Al Jazeera speaks to Ben Barnes, chief of the Shawnee Tribe and a NABS board member, about why the group is supporting the bill and what effects it would have on survivors of the boarding schools, their families and their communities.

Al Jazeera: Why is the understanding of the legacy of Indigenous boarding schools incomplete?

Ben Barnes: I think they’re incomplete nationally because they’re incomplete in our own homes. It is incomplete inside of our own tribal nations.

When those boys and girls [sent to boarding schools] became adults, there was an idea they brought back to their homes: Don’t be too Indian. Don’t speak your language.

There were things those children endured … It’s very hard for little boys who were sodomised to come out and tell those stories. In all communities, those are not stories that people have an easy time telling.

So [the work of advocates] has been about creating this place of understanding for folks that attended these places to tell their stories. And for many, they’re already 80 years old. When else will they tell it?

Al Jazeera: What about from an institutional perspective?

Barnes: It really ranges across a big spectrum. Some of these [schools] were privately run … Some were religiously run, others were federally run institutions.

In some cases, the willingness [to provide records and information] is there, but the actual institutions have never put any money and effort towards making the information accessible… And if institutions have information that’s embarrassing, they’re going to want to withhold those records.

And in some cases, there are people that are culpable, that created or performed criminal acts on children. That information is not going to be handed over to us willingly.

We do not want the truth sifted through a sieve so that we can only get granulated truths. We want to see it ourselves and create our own record.

Al Jazeera: In that case, why is this legislation, particularly the subpoena power, so significant and separate from the federal investigation?

Barnes: The Department of Interior only has access to records of federally run and funded institutions, like the Carlisle boarding school [a former boarding school in Pennsylvania where the graves of 187 Indigenous students have been found].

However, there’s nothing in Interior’s pockets for, for instance, a labour camp run by Methodists or for a baby mill run by some people in southeast Oklahoma … Are those boarding schools? For our purposes, yes, they are — but they’re definitely not the idea of a boarding school as [the Interior Department] understands it.

So we’re still finding new institutions. We’re still finding new boarding schools. The numbers keep changing. And we want to be able to subpoena county and local city records and private records of organisations … In some instances, we’re going to have to compel those records.

Al Jazeera: Why is this important now?

Barnes: We’re running out of time for a lot of these survivors.

Martin Luther King Jr said, ‘Injustice anywhere is a threat to justice everywhere.’ So these folks, because of their age, are we going to deny them justice?

At what age do we stop seeking justice for people? How long ago does the pain have to be? Last week? Last month? Last year?

I confess that I didn’t have much understanding, personally, about what intergenerational trauma really was. To me, it was just a phrase. Perhaps even in my mind, I’ll confess, I thought maybe it was an overused phrase until I started talking to survivors.

Those aunties and uncles that came away from boarding schools were changed by it. They were hardened, or they were disciplined, or they were emotionally unavailable.

They went into these places as little children, and they didn’t learn how to be a mother: They learned how to be a matron. They didn’t learn how to be a father: They learned how to be a supervisor. And some of those children also learned how to be brutal.

They brought those things back into their adult homes once they got out of boarding school … So there’s trauma that we have to examine because it goes towards trying to understand [the] treatment.

These things are important, not just for healing, not just for some noble cause, but they can also affect policy.

Al Jazeera: What has the receptivity been from US legislators?

Barnes: I am hopeful. Whenever we sit down to have these conversations, everyone understands. And the Republicans and Democrats on the Senate Committee of Indian Affairs understand.

But there are political realities for any bill trying to get pushed through the House and the Senate.

We just need to make sure that we do our ground game, to make sure that everyone knows why this bill needs to be passed, and we’ll continue doing that as the House and Senate returns to DC [after their August break].

It is also important to keep this out of the realm of Republican politics or Democrat politics. It’s not about that. This is a nonpartisan issue.

This interview has been edited for length and clarity.