The lawsuit, obtained by TMZ Sports, was filed in a federal court on Friday by Jamea Harris' mother, DeCarla Heard ... nearly 10 months after Harris was allegedly murdered by Miller's friend.

In the suit, Heard claims Miller played a significant role in her daughter's Jan. 14 death ... alleging Miller was the one who came to the location of the shooting with the firearm that Michael Davis then used to kill Harris.

Heard claims Miller, Davis and former Tide basketball player Darius Miles had all been together earlier in the night at a row of clubs in Tuscaloosa, when Miller left because a line to get into one of the bars was too long. She says Miles left his gun in Miller's ride before the basketball phenom took off.

A short time later, though, Heard says Davis and Miles left the bar ... and got into a dispute with Harris, her boyfriend and her cousin. She claims in the suit Miles then texted Miller, now a Charlotte Hornet, asking for his "joint" because "someone was 'fakin',' meaning using words in an aggressive manner with no intention or ability to back them up."

Heard says when Miller showed up minutes later, Miles then retrieved the gun from the hooper's ride, before he handed it off to Davis. She alleges Davis then approached Harris, her BF and her cousin in a car and fired off rounds -- striking Harris with at least one in the face, killing her.

Heard is seeking damages ... claiming Davis, Miles and Miller "should have known that bringing a dangerous weapon to a dispute and discharging said weapon would likely result in harm to those around them."

For his part, Miller's attorney said in February that Miller "never touched the gun, was not involved in its exchange to Mr. Davis in any way, and never knew that illegal activity involving the gun would occur." He was never charged with a crime.

As for Miles and Davis, both are facing capital murder charges over their alleged roles in Harris' death.