A teenager was arrested after police said he shot another teenager last year during a drug deal in St. Petersburg.

The 16-year-old boy is facing first-degree murder charges in the death of Donald Avery, 17. Avery was shot and killed in the early morning hours of Oct. 11, 2014.

According to St. Petersburg police, a passerby reported hearing a gunshot coming from the pedestrian overpass that crosses 34th Street S in the 700 block. The passerby discovered Avery on the overpass. He had been shot in the upper body.

The passerby called 911, and Avery was taken to Bayfront Health St. Petersburg, where he was pronounced dead.

Investigators said they determined the teenage suspect met Avery at the overpass to conduct a drug deal. At some point, investigators said the teenager pulled out a handgun and shot Avery several times.

Police said a motive for the murder has not been determined.

Investigators said the teenager denied any involvement in the shooting when he was initially questioned and that a short while later, the teen's family moved him from St. Petersburg to La Belle, in South Florida.

On Monday, detectives arrested the teenager at La Belle High School on the outstanding warrant for first-degree murder.

Police said that shortly after the teenager was arrested, Karissa Ann Smock, 18, apparently called a witness in the case and threatened to kill him. She was arrested Monday on charges of tampering with a witness.

The murder suspect is not being identified as it is not yet known if he will be charged as an adult.