Police say 29-year-old Troy was robbed and fatally shot August 28 at a home in Wake Village, Texas.
The case is being investigated as capital murder.
Robinson's mother, LaDonna Robinson, last talked to the 29-year-old the same day he was shot.
The mother says she doesn't know why anyone would shoot her son, but she wants justice when it comes to whoever is responsible for her son's death.
"They didn't have to shoot him like that. He didn't have (anything) for them to take. He didn't own his own house...All he had was him," Robinson said.
"Why did they have to kill him? That's what I want to know," said Trineisha Robinson, who is Troy's sister.
Wake Village Police say no suspects have been arrested as of Tuesday. The investigation continues.
Police had been looking for two people of interest who may have been in contact with Robinson before his death.