Johnson, who lived alone, was found dead on Sept. 15, 2015, detective Andrea Branch said Tuesday.

“He was killed 10 days before his 23rd birthday,” Lynn Perez said Tuesday.

“Alex was my first-born. I had him very young,” Perez said. “We kind of grew up together like friends. You have your issues when they become teenagers and young adults but —” her voice caught — “Alex and I were very close.”

Police don’t want to provide many details, including a potential motive or the cause of death, and don’t want to say how long Johnson was dead except to say it was hours rather than days.

“I feel as if it was just a simple, stupid robbery,” Perez said. She said the killer “maybe knew of him (Alex), or was a ‘friend of a friend,’ or (part of) a circle of friends.” She said that might make it harder to find his killer, but that the reward might help.

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