"The stark, staggering fact is that the nation has no reliable idea how many Americans die during arrests or police custody each year," the statement, released Thursday, said.
"This legislation will fix that unacceptable factual gap. It will ensure that the nation knows exactly how many Americans die in custody, and it will give the information needed to strengthen trust at every level," the statement added.
The bipartisan "Death in Custody Reporting Act", which passed the Senate on Wednesday, is now waiting for US President Barack Obama's signed approval.
The bill follows recent US grand jury decisions not to indict white police officers who were responsible for the deaths of two African-American men this summer.
One of the African-Americans, Eric Garner, was killed in a chokehold by officer Daniel Pantaleo in New York in July. The other, 18-year-old Michael Brown, was shot to death in August, in Ferguson, Missouri, by officer Darren Wilson.
Both of the incidents as well as the grand jury decisions have led to massive protests across the United States.