The 14-year-old girl is charged as a juvenile.
Martin was walking home from Tilden Career Academy in the 900 block of West Garfield when the shooting took place around 4:30 p.m. Monday.
She was shot in the back. Another teen girl was shot in the arm. Martin was taken to Comer Children's Hospital, where she later died. The other victim was taken to St. Bernard Hospital, where she is listed in stable condition. She is expected to recover.
Chicago Police said an altercation took place among a group of teens standing on the sidewalk before someone opened fire on Monday. One witness said the group only consisted of girls. "All girls," Kirk Peals, a witness to the fight, said. "Kids. Nobody over 15. Everybody was young. Babies."
Martin's parents, Kent and Joanie Kennedy, believe it was a girl from another school that gunned her down. They said this is something they never thought possible, for an online fight to escalate to their daughter being shot and killed.
"Never, never would imagine one of our kids would be gunned down like this," Kent Kenndy said. "For what? She wasn't a gangbanger. I mean, it just boggles my mind."
Grief counselors will be on-hand at Tilden Academy Tuesday, as other students learn of their classmate's death. Martin's parents said she recently transferred to Tilden in order to have a shorter, safer commute to and from school.
"It's senseless. Kids are dying so young nowadays. Senseless," Kent Kennedy said. "Parents shouldn't have to bury no child. No child."
Endia's step-father said she was a good kid who didn't run with the wrong crowd. He said she had a kind heart. She wanted to travel and see Paris and Italy, loved to dress up and change her hairstyles, and competed on the street and in school in footwork dance contests.
As the 14-year-old's family left the hospital, they made a plea for the killers to turn themselves in.
"Just give it up. Turn yourself in," Joanie Kennedy said.
"No child needs to be gunned down like a dog in the street. Nobody, period," said Kent Kennedy.
Officers interviewed a person of interest in connection with the shooting overnight. Police had not made any arrests as of Tuesday morning. The investigation continues.