By Joe Holden

PHILADELPHIA (CBS) —  Aug. 1, 2007. This date is forever etched in the heart and mind of a local mother. It was the last day she saw her son alive. Fifteen years later, she needs your help to find her son’s killer.

It was a sweltering summer night, and Eric Woods was leaving to play basketball.

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“His favorite thing was basketball, and he loved people,” Monique Irvis said.

Out the door of his South Philadelphia home he went. Irvis remembers that final conversation.

“I felt bad because I fussed at him before he left because I was like, ‘don’t forget to come back and put the trash out,'” Irvis said, “and he said, ‘all right mom,’ you know.”

That was the last time Irvis saw her 19-year-old son alive. That was Aug. 1, 2007.

Woods was shot and killed walking home from the basketball game.

“It’s like 15 years of pain, 15 years of anger,” Irvis said.

Philadelphia police have had a difficult time making headway with the investigation. There’s no surveillance video. The shooting happened near the intersection of Springfield Avenue and Divinity Street in Southwest Philadelphia. The area was dimly lit.

Investigators on Wednesday told CBS3 Mysteries the shooter mistook Woods for somebody else. Plainly, they shot the wrong guy.

“I’m very angry. I’ve been trying to say I’m not angry, I don’t know,” Irvis said. “It just angers me. It’s been too long.”

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Irvis is angry. The passage of time has done little to heal deep wounds. She takes us back to the night her son lay dying in a hospital bed. She says doctors would not allow her to say goodbye.

Irvis remembers a doctor approaching her.

“I could see him walking to me and all I knew was he must have said he’s not here anymore or whatever, but I blacked out and I ran out,” she said. “It was just black and I just fell to the ground outside.”

She says her attempt to say one last goodbye was dismissed.

“It’s the worst feeling not to be able to see your child, especially after something that tragic,” Irvis said.

Irvis is frustrated with the Philadelphia Police Department and what she describes as a lack of compassion.

“Do they understand that the pain never goes away? Do they understand the anger never goes away? The hurt? There are so many things that don’t go away,” Irvis said.

There are two days each year that Irvis braces for — Aug. 1, the anniversary of her son’s death, and Christmas, Woods’ birthday. He would have been 34 this year.

Does she have hope that someone can come through for her and her family?

“I’m trying to have hope, but I don’t have any,” Irvis said. “I don’t have any hope in the system.”

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Do you have information on the homicide case of Woods? Call 215-686-TIPS. There is a reward.