Mann was convicted in 2018 of murdering a retired STL police sergeant

ST. LOUIS — Prosecutors reached a plea agreement Monday with a 20-year-old who shot and killed a retired St. Louis police sergeant as a teenager in 2018.

Jalynn Garner was scheduled to go on trial this week for the murder of Ralph Harper. Garner was charged with first-degree murder, first-degree robbery and two counts of armed criminal action.

Garner previously pleaded guilty to these charges in 2019 but was allowed to withdraw these allegations. At the time, defense attorneys argued that Garner had pleaded guilty to violating an eligibility deadline for the dual-jurisdiction program; Garner was later determined to be ineligible.

The agreement with St. Louis prosecutors allowed Garner to plead guilty to second-degree murder; The remaining charges remained unchanged.

Garner and Justin Matthews, both Confluence Academy students, were 15 and 16 years old, respectively, when they attempted to rob Harper on the morning of Oct. 29, 2018, in the city’s Tower Grove South neighborhood.

The teens approached Harper after he parked his car in the 3100 block of Lackland Avenue. Harper, who retired from the St. Louis Metropolitan Police Department in 2007 after more than 30 years on the force, was on his way to babysit two of his family’s children.

Harper exchanged fire with Garner but was fatally wounded. Harper was 67.

Garner was shot in the arm and fled with Matthews in a stolen vehicle. The teenagers later crashed and were arrested.