Story highlights An ad for Bernie Sanders featuring the daughter of a man killed by police highlights criminal justice system abuses, says Cid Martinez

Erica Garner is campaigning for Sanders in South Carolina

Cid Martinez is an assistant professor of sociology at the University of San Diego and author of the forthcoming book "The Neighborhood Has Its Own Rules: Latinos and African Americans in South Los Angeles." His work focuses on criminology, policing, religion, urban politics, immigration and race relations. The opinions expressed in this commentary are his.

(CNN) Last week, Bernie Sanders' campaign released a four-minute video ad featuring an endorsement from the daughter of Eric Garner, the New York man who was choked to death by New York City police officers. In the course of the ad, Erica Garner talked about her father's death as unjust and its effect on her and her young daughter.

Cid Martinez

Garner's support comes at a key time in the election, as Sanders and Hillary Clinton , his rival for the Democratic nomination, seek to rally support among African-American and Latino voters in the upcoming primaries.

The video raises the urgent issue of the broken criminal justice system and its effects on American society, a topic few liberals want to address through activism. How do we know it's broken? According to Harvard sociologist Bruce Western in his book "Punishment and Inequality in America," the United States is the world's leader in incarceration, with more than 2.2 million people behind bars. Western notes that in the past 30 years, incarceration has increased sevenfold.

Police-involved shootings are another sign that the system has unraveled. Although there is not good data quantifying the number of police-involved shootings, since law enforcement does not collect this information, many criminologists would say there is a disproportionately higher number of police-involved shootings of blacks and Latinos.

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