Tony De La O, a member of the Rayburn High School football team and ROTC, had just celebrated his 18th birthday when he was killed on Jan. 20, 2025.
Last summer, Clint Gillespie and Rodesha Smith were charged with capital murder in De La O's death.
On Monday, police arrested Isiah Goodwin and charged him with engaging in organized criminal activity.
Prosecutors say he took part in multiple armed robberies with Smith and Gillespie from November 2024 to January 2025 and was present when the murder took place.
"That was kind of mind-blowing. It's crazy to think there's kids out there setting up people," said the victim's sister, Kasandra De La O.
The day of the murder, police say Smith lured De La O to an apartment complex on Hollock Street in southeast Houston under the guise of wanting to buy weed from him.
Instead, police say he was shot and robbed.
As he attempted to flee the scene in his car, police say Goodwin and another person fired shots at him.
"They didn't care that he was hurt. They didn't care what happened to him after. They just didn't care," said Aislynn Martinez, the victim's fiancé.
A search warrant Eyewitness News obtained reveals Goodwin was interviewed by police a month after the murder, although he wasn't charged until June of this year.
Within two hours of the murder, police say Smith messaged someone about selling a gun.
"I need it gone fast," she's quoted as saying, to which the other person replies, "That hot huh?"
Smith was charged with another robbery months before De La O's murder.
Police say she arranged to meet a man to purchase a cell phone that he had posted online. But instead of paying for the phone, they say she pulled a gun and stole it.