Jury selection is underway in a murder charge against former police Minneapolis officer Derek Chauvin, who is accused of killing George Floyd by choking him during an arrest for an alleged petty crime in May of last year, as authorities cast a wary eye on potential civil unrest during and after the trial.

The county medical examiner in the state of Minnesota last year ruled Floyd's death a homicide caused by "cardiopulmonary arrest complicating law enforcement subdual, restraint and neck compression." Floyd suffered from heart disease and had drugs in his system, The Wall Street Journal reported.

The defense has argued that the drugs and heart disease caused the death, not excessive force.

Floyd's death sparked riots in the city of Minneapolis and elsewhere in the U.S., in protests against what many said was an example of excessive force routinely used by white police officers against black suspects.

Minnesota Attorney General Keith Ellison is leading the prosecution, which is still in flux as it awaits higher court rulings on possible other charges. Chauvin faces second-degree murder charges of unintentional death while committing a felony-and second-degree manslaughter.

Three other officers on the scene on May 25, 2020 were charged with abetting second-degree murder and manslaughter, and are expected to face trial in August. All four officers have pleaded not guilty.

The state had initially charged Chauvin with third-degree murder, which involves a reckless act that threatens the lives of others. The state later added the second-degree murder and manslaughter charges.

The judge overseeing the trial, Peter Cahill in October dismissed the third-degree charge on grounds that the statute applies only when more than one person is threatened by the act.

Jury selection allows the defense and prosecution to ask questions and strike a limited number of prospective jurors based on the answers. The jury selection process could last as long as two weeks, with opening arguments scheduled for March 29. The trial is expected to take two to four weeks.