An autopsy on the body of the black teenager shot and killed by white St. Louis police officers this week shows the 18-year-old died from a single gunshot wound in his back, police said on Friday.

The results of the autopsy by the city’s medical examiner in the death of Mansur Ball-Bey are preliminary and an investigation of the incident continues, police said in a statement.

The finding may escalate tensions that flared immediately after the shooting Wednesday, as protesters and family members of the slain teen questioned police accounts that Ball-Bey pointed a gun at them as he fled from a home where police were serving a search warrant.

St. Louis Police Chief Sam Dotson told the St. Louis Post-Dispatch newspaper that the location of the fatal wound neither proves nor disproves the account given by the two officers who said they fired four rounds at Ball-Bey.

The shooting sparked angry clashes between residents and police Wednesday night, with officers turning out in riot gear and using tear gas on some protesters.

The flare-up comes less than two weeks after the St. Louis area was flooded with protesters from around the country marking the anniversary of the Aug. 9, 2014, police killing of unarmed black teenager Michael Brown by a white police officer in nearby Ferguson, Missouri.

Brown’s death was one of a series of police killings of unarmed black men and teens across the United States that sparked a newly energized civil rights movement under the banner “Black Lives Matter.”