Two Missouri teenagers were arrested Monday in connection with the fatal shooting that morning of a 67-year-old retired St. Louis police sergeant after a botched robbery attempt, authorities said.

The teens, ages 15 and 16, were charged with second-degree murder and attempted robbery, among other charges, FOX 2 of St. Louis reported. The 16-year-old is believed to have been the gunman, according to the St. Louis Post-Dispatch.

A third teen, age 17, was also arrested but police said he was not involved in the robbery. He was charged with misdemeanor vehicle tampering and resisting arrest, FOX 2 reported.

Police Sgt. Ralph E. Harper, who retired in 2007 after 33 years in the department, was parking his car around 7:30 a.m. near a park in St. Louis, when an armed robber approached him, the Post-Dispatch reported, citing police. Harper, who was armed, engaged in a shootout with the suspect.

He was on his way to babysit for a relative, a friend told FOX 2.

"It hit very close to home, because I knew the sergeant personally," St. Louis police Chief John Hayden told reporters, according to the Riverfront Times. "We're all mourning together."

"It hit very close to home, because I knew the sergeant personally. We're all mourning together." 

— St. Louis police Chief John Hayden

A getaway vehicle took the 16-year-old to a nearby hospital to get treated for a gunshot wound to a wrist. Police arrested the 15-year-old and 17-year-old after they crashed the vehicle, according to the Post-Dispatch.

Police found a gun believed to be the murder weapon inside the vehicle, along with blood, the Post-Dispatch reported, citing a law enforcement source.

Harper called  911 himself and died shortly after being taken to a local hospital.

The 17-year-old was involved in a drug and weapons case just a week earlier and was released from custody as police awaited additional evidence, FOX 2 reported.

The two younger suspects are juveniles, so their names are not public. However, Marissa Woods revealed the identity of the 16-year-old as Justin Mathews, her son, and brother to Julian Mathews, according to the Dispatch.

It is unclear whether the two juveniles will be charged as adults.