In an interview from Miami, Curt Obront said his client Marc Wabafiyebazu, 15, of Ottawa, had an unblemished past until the incident on Monday that left two people dead, including his older brother Jean.
"This is literally a first time he's had any contact with the criminal justice system anywhere," Obront said.
Obront refused to discuss any specifics of the case.
"The case is a tragedy. Our hearts certainly go out to the families of the teenage victims who tragically lost their lives," the lawyer said.
"He's lost his brother. It's a difficult time for everybody."
Wabafiyebazu, who remained in youth custody, has yet to be formally charged, Florida state authorities said.
"The case has just started," Ed Griffith, spokesman for the Miami-Dade Office of the State Attorney, said.
"We're evaluating all of our legal options at this point."
Other decisions to be made — if he is prosecuted — include whether to try him as a youth or an adult.
"Given the potential implications to some of this, we will very carefully make the appropriate charging decision but we have time," Griffith said. "The whole matter is under review."
The Wabafiyebazu brothers had only recently moved to Florida to be with their mother, Roxanne Dube, an experienced diplomat who became Canada's consul general in Miami six weeks ago.
In a statement, Dube expressed condolences to the family of Joshua Wright, the other deceased victim.
"Your grief is our grief," she said. "We can only hope that, in time, we will find common purpose towards diminishing the causes of such violent crimes. For now, we just want to be there for Marc, our incredibly caring son who loved his brother very much, and to say goodbye, ever so tenderly and quietly to Jean, our love."
According to the arrest affidavit, Miami police responding to a shooting found a dead person inside a home with "what appeared to be multiple gunshot wounds" and Jean Wabafiyebazu, 17, who had been shot at least once and died in hospital.
Citing witnesses, police allege that Jean Wabafiyebazu had called Anthony Rodriguez, 19, of Miami, about buying 900 grams of marijuana. Rodriguez then drove to the home, as did the Wabafiyebazu brothers, who reportedly used their mother's BMW with diplomatic licence plates.
Rodriguez and the older brother went inside to make the deal while the younger brother waited outside the apartment complex, according to police and local reports.
"During the negotiations, both deceased victims became involved in an exchange of gunfire," according to the complaint against Rodriguez, who police have charged with second-degree murder and possession of marijuana for the purposes of trafficking.
Two others, including Rodriguez, were shot and injured in the melee.
Neither police nor state authorities were able to confirm that Wabafiyebazu was being held on suspicion of felony murder — an allegation that implies indirect involvement in the actual killing.
Investigators also accuse Marc Wabafiyebazu, who turned 15 two weeks ago, of allegedly threatening to kill an officer by shooting him in the head at Miami police headquarters.
If formal charges are laid, Obront said his client will plead not guilty.
"We will be defending the case and look forward to having our day in court," the lawyer said.
In the most severe circumstances, Wabafiyebazu's sentence would have to end when he turns 23 if convicted as a juvenile. If convicted as an adult, he could face a much harsher sentence, but not the death penalty.
The brothers' father Germano Wabafiyebazu, who is divorced from their Dube, said he was awaiting release of his son's body so he could organize a funeral.
"I'm very, very sad," he said Thursday.
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