Reuters

CHARLESTON, S.C.

Trials in two South Carolina shootings that rocked the country last year and raised questions about race in America started last week, putting the city of Charleston on edge as the community awaits the testimony and jury decisions.

Jury selection continued Nov. 7 in the federal death penalty trial of Dylann Roof, a white supremacist who was charged with federal hate crimes after the shooting deaths of the pastor, Clementa Pinckney, who was a state senator, and eight parishioners during Bible study at historic Emanuel African Methodist Episcopal Church in June 2015.

The proceedings getting underway at the U.S. courthouse in Charleston unfold as another racially charged trial progresses across the street. Michael Slager, a white former police officer in North Charleston, is being tried for murder in state court in the shooting death of black motorist Walter Scott in April 2015.

Black community activists said the outcomes will test the calm that prevailed after the shootings and could trigger unrest if those angry about the killings feel justice is not served.

“The community is, for lack of better words, on eggshells,” said Justin Bamberg, a state legislator and lawyer who represents Mr. Scott’s family.

Both trials are expected to last several weeks and draw national attention to the port city of about 133,000 people that is known for its cuisine and well-preserved 18th- and 19th-century architecture. But Mr. Bamberg said the cases have important distinctions.

Mr. Roof’s trial is less about his guilt or innocence than whether he will be sentenced to life in prison or death, Mr. Bamberg said. Mr. Roof’s lawyers have said he would plead guilty to 33 counts of hate crimes, obstruction of religion and firearms charges if prosecutors agreed not to seek the death penalty.

Mr. Slager’s case, on the other hand, could produce a rare result: A guilty verdict against a police officer charged with murder or manslaughter.

Since 2005, 27 of the 77 officers charged across the country with murder or manslaughter after an on-duty fatal shooting were convicted, according to Philip Stinson, a Bowling Green State University associate professor who tracks such cases.

Twenty-nine of those criminal cases ended with no conviction, while cases for 21 of those officers, including Mr. Slager, are pending.

The North Charleston case triggered national concerns about racial bias in law enforcement, with both trials underscoring concerns about equal justice in the United States.

“Our confidence level in the justice process working is like sitting on pins and needles,” said Edward Bryant III, president of the NAACP branch in North Charleston, where black residents have long complained of racial profiling by the largely white police force.

Mr. Slager was arrested and charged with murder after investigators watched a bystander’s cell phone video that showed him firing eight times at the back of 50-year-old Mr. Scott as he fled from the officer.

Defense lawyers say the video does not show the whole story of what happened after Mr. Scott was pulled over for a broken brake light. They will argue that Mr. Slager, who has pleaded not guilty, felt threatened by Mr. Scott as the men struggled over the officer’s stun gun.

The defense has asked for Mr. Slager’s trial to be moved to a different venue, saying the security measures needed to preserve order amid the two, high-profile proceedings will make the area around the courthouses look “more like an armed camp than the Holy City.”

“The juxtaposition, both temporally and territorially, of the United States v. Dylann Roof trial taking place literally across the street simultaneously with Slager’s trial will no doubt bring a media spectacle to rival any ever seen in this or any town, in addition to hordes of supporters, detractors and community activists from every philosophical bent,” Mr. Slager’s lawyer, Andy Savage, wrote in a motion that has not yet been taken up.

Law enforcement officials have asked the community to help keep things under control during what Charleston Police Chief Gregory Mullen said would be “a very delicate and important time for the city.”

Local civil rights leaders and lawmakers said they fear what might happen as the trials conclude, particularly if jurors find Mr. Slager not guilty.

“We will let justice work, but if people perceive that justice doesn’t work, you’re not sure where this is going,” said Dot Scott, president of Charleston’s NAACP chapter. “There’s quiet rumbling right now.”