Family of Alton Sterling expresses frustration after decision to not pursue criminal charges against police officers.

A prosecutor in the US state of Louisiana has ruled out criminal charges for two white police officers in the 2016 killing of African American Alton Sterling, whose shooting triggered nationwide protests against police brutality.

Louisiana Attorney General Jeff Landry said on Tuesday that following an investigation the state could not proceed with a prosecution of police officers Blane Salamoni and Howie Lake.

“This decision was not taken lightly,” Landry told a press conference.

Sterling, a 37-year-old father of five, was held down by the two officers and shot dead outside a convenience store in Baton Rouge on July 5, 2016.

The incident, which lasted for less than 90 seconds, was captured on a cellphone video.

Sterling’s killing occurred amid national outrage at deadly violence from law enforcement that disproportionately impacted minorities in the US.

US Representative Cedric Richmond said the incident was “deeply disturbing” and called for an investigation.

Protests were expected in Baton Rouge and across the US following the decision.

Sterling’s aunt, Sandra Sterling, condemned the decision to not charge the police officers.

“You put a killer back on the streets,” Sterling said, according to reports.

During a news conference also on Tuesday, Quinyetta McMillon, mother of one of Sterling’s children, reportedly said that the way the officers killed the 37-year-old was “in cold blood”.

In May 2017, the US Department of Justice announced it would not press charges against the officers.

During a 10-month probe, FBI agents and prosecutors reviewed images of the incident captured by body cameras, mobile phones and store surveillance cameras as well as witness accounts and other evidence.

At the close of that investigation, the justice department said it found “insufficient evidence to support federal criminal charges” against either officer.