The shooting took place in Eastern Market -- just blocks away from Ford Field -- as people were partying after the Lions had just lost a heartbreaker to the Tampa Bay Buccaneers.

Cops said a preliminary investigation revealed that 25-year-old Jalen Welch had gotten into a dispute with a 40-year-old man at the venue ... when the man opened fire and killed him. A bystander, police added, was also struck by the gunfire ... and later died at a nearby hospital from his injuries.

But, according to Wayne County Prosecutor Kym Worthy, a further probe into the matter revealed Welch appeared to be the aggressor ... and the 40-year-old was merely protecting himself.

"We have reviewed this case thoroughly," she said in a statement Wednesday afternoon, "and this is a case of lawful self-defense. It is absolutely tragic that during all the fun and merrymaking at a Lions tailgate that, two lives were lost. The first was Mr. Welch, who was the one who first pulled out a gun and was shot by the 40-year-old, a lawful CPL holder, who was defending himself. A single shot was fired."

"And then," Worthy continued, "perhaps the most heartbreaking of all is the fact that a completely and totally innocent bystander, Mr. [Rayshawn] Palmer, was shot and killed with the same bullet that passed through the head of Mr. Welch. It could have been any one of us. We looked at all the applicable laws, and there is no crime that can be charged or proven beyond a reasonable doubt."

Eastern Market officials, meanwhile, said they are putting a pause on the tailgating festivities for the Lions' next home game on Sept. 30 "out of respect for the victims and their families."

"Following the pause on September 30th," they added, "we intend to resume the tailgating tradition for the remainder of the season after enacting additional and significant security protocols that will be communicated to the public in advance."