EVANSTON, Ill. (CBS) -- Margaret Miller Johnson, one of the four people shot and killed on a Chicago Transit Authority Blue Line train this week, is remembered for her sweet demeanor and beautiful smile.

Simeon Bihesi, 28, was a former Marine who hoped to one day be a Columbus police officer. He was among 4 killed in a mass shooting Monday in Chicago.

Three people have been charged in connection with the March 20 shooting death of 28-year-old Chicago letter carrier Mechella Williams, whose bullet-riddled body was found in a car parked in Orland Park,

Mechellea Williams, a mother of three was found dead inside a vehicle in March in Orland Park. She lived on the Far South Side. The three suspects were arrested in August.

While specific circumstances may differ from one event to another, the most pressing questions are the social roots of these repeated outburst of violence and how to stop them from happening.

A Southwest Side man has been charged with murder in connection with an April shooting that killed 9-year-old Ariana Molina and wounded 10 of her relatives, authorities said. Octaviano Romero, 39 and a resident of the New City neighborhood,

Three people have been charged in connection with the murder of a mother of three who worked as a mail carrier in Chicago.

Three people are in custody in connection with a mail carrier's shooting death in Orland Park earlier this year.