Officials say Aniah Blanchard was killed by a gunshot ... and now, they're seeking the death penalty for her alleged killer.
Blanchard's body was recovered in a wooded area in Macon County, Alabama on Nov. 25 after she had gone missing for weeks.
The medical examiner conducted an autopsy and determined Blanchard -- the stepdaughter of UFC fighter Walt Harris -- was killed by a gunshot ... but didn't specify to which part of her body.
Now, prosecutors say the man accused of pulling the trigger -- Ibraheem Yazeed -- is being charged with capital murder, and they're seeking the death penalty.
"This case has shaken our community to its core," Lee County District Attorney Brandon Hughes said Monday ... "It is my intention that the response to this horrific crime serve as a warning to anyone who believes they want to come to Lee County and engage in violent criminal behavior."
Hughes added, "You will be dealt with and the consequences will be severe."
So far, three men have been arrested in connection with Blanchard's abduction ... but Hughes said Monday Yazeed is now believed to be the "lone person responsible" for Blanchard's death.
Hughes says Yazeed abducted Blanchard from an Auburn gas station on Oct. 23 ... and his first-degree kidnapping charge has now been upgraded to capital murder.
Yazeed is still being held in jail without bond.
As for Blanchard's family, her mother, Angela Harris, emotionally spoke about the tragedy last week ... while Walt Harris penned a thank-you note to Aniah on social media, writing, "This pain is unbearable."