ORLANDO, Fla. — There’s a person of interest, but no arrest in the killing of a student a year ago. 

On Wednesday, the Orange County Sheriff's Office explained why.

Investigators say Alejandro Vargas, known as Alex by friends and family, was making his morning walk to Boone High School on December 18, 2018, when he was gunned down.

Donte Singletary says whenever he passes a memorial to Vargas on his way to school, he can’t help but pray.

“I pray for his family because I see the photos of his mom,” Singletary said.

Singletary thinks about what it must be like for Vargas’s mother, one year after the 15-year-old was taken from her. “I just look at the pictures and it makes me sadder, because I have a mom, and I don’t know how she feels right now. I can only imagine.”

Singletary says he still remembers the morning of Vargas’s killing.

“I have a little brother his age, it could’ve been him,” said Singletary. “When I heard a 15-year-old got shot at Boone, my brother was walking that day.”

It wasn’t his brother. But the relief of finding that out didn’t stop Vargas’s killing from making his heart ache even now, one year later.

He says his little brother also knew Vargas.

“And it makes me sad because he never did anything to nobody, he’s a cool kid. It could’ve been easily my brother,” said Singletary.

Spectrum News 13 first reported back in the summer that court documents show the state attorney’s office wants to use evidence against 19-year-old DeAndre Florence to charge him in Vargas’s killing.

On Wednesday, the Orange County Sheriff's Office said it was still building a case against Florence and was not rushing. 

Sheriff John Mina said Florence and another man, Denim Williams, were driving a stolen vehicle when they shot Vargas.

Investigators believe Williams and Florence spotted Vargas on a phone and decided to rob him. That's when he was shot. 

Mina says Florence is already in jail in connection to the death of Denim Williams. The sheriff's office said Williams died 2 weeks after Vargas's death when he was shot by an alleged target during another cell phone robbery. 

Florence is awaiting trial in that case, as part of the state's felony murder rule, and is in jail on no bond status.

Meanwhile, Singletary is left mourning the loss of his brother’s friend – and left wondering why.

“There’s no reason to do this, this has to stop. Kids are dying younger and younger, and I don’t like it,” said Singletary.

Information from Reporter Asher Wildman contributed to the story.