A prosecutor says no charges will be filed against an off-duty white police officer who shot and killed a black 18-year-old in October.

St. Louis Circuit Attorney Jennifer Joyce's report, released Monday, says a criminal violation could not be proven beyond a reasonable doubt in the killing of VonDerrit Myers Jr.

The police officer, who was not named in the report, was patrolling a neighborhood near the Missouri Botanical Gardens as a security officer when he approached Myers.

The report says the officer had reason to suspect Myers was armed and a chase ensued.

Authorities said Myers fired at least three shots at the officer, who returned fire.

Myers' death fuelled protests, coming two months after the killing of black 18-year-old Michael Brown in the St. Louis suburb of Ferguson.