Their elder son Jean, 17, was killed Monday, while their younger one, Marc, 15, was arrested in connection with what local media outlets have characterized as a marijuana deal gone wrong.
Germano Wabafiyebazu said he sat his sons down in early February before they moved from Ottawa to Miami with their mother, Roxanne Dube, who is Canada's top diplomat in Florida. Wabafiyebazu and Dube are divorced.
He said he spoke to the teens "at length" about the potential risks of life in Miami and urged them to take extra care in some neighbourhoods and when dealing with police, particularly since they're black.
"They forgot the warning that I gave them, the caution that they should have taken," Wabafiyebazu said Wednesday in an interview in Ottawa.
"That's what must be torturing Marc. He's crying because his big brother is dead."
Wabafiyebazu wanted the pair to stay in Ottawa, where they were born and raised, and only travel to Miami from time to time to see Dube. In a separate interview with The Associated Press, he said Jean struggled with substance abuse.
The boys, however, were thrilled to move to Miami with their mother, particularly in the middle of this year's harsher-than-usual winter, he said.
Dube, who served as ambassador to Zimbabwe from 2005 to 2008, began her Miami posting as Canada's consul general only six weeks ago. She also worked as an assistant to former Liberal cabinet minister Lloyd Axworthy, according to media reports.
"She's certainly the one who's the most directly affected in this because she's the one who brought them there," said Wabafiyebazu, when asked how his ex-wife is coping.
"I'm in a very bad state. Listen, to see an 18-year-old child who was suddenly killed. When someone is ill, you can gradually get used to the idea that there's no hope, but this is a child in good health, so it's a shock."
Wabafiyebazu said he was advised by a family lawyer Wednesday to stop talking to the media about the incident or his sons.
Two people were killed during the incident, including Jean Wabafiyebazu, according to local media reports that said a fourth male was wounded and was later found at a gas station.
The diplomat's car has been seized in the investigation, multiple sources say.
The boys drove their mother's BMW to the scene of the crime, reports said. The younger son reportedly waited outside with the vehicle, which had diplomatic plates although it was not the official embassy car.
Meanwhile, gunfire broke out inside the adjacent apartment complex.
The Miami-Dade State Attorney's Office confirmed to The Associated Press that another man, 19-year-old Anthony Rodriguez, has been charged with second-degree murder and marijuana possession with intent to sell.
The Rodriguez arrest report says a second man was shot to death inside the house, but it did not identify him. Prosecutors also said Rodriguez was wounded in the arm in the shootout.
The police report also quotes unidentified witnesses as saying Rodriguez brought two pounds of marijuana to the house and began to negotiate.
"During the negotiations, both deceased victims became involved in an exchange of gunfire," the report says.
Marc Wabafiyebazu faces charges of threatening a police officer while in custody, according to a separate police report obtained by AP. The boy is alleged to have said "he was going to kill (a detective) and that he would shoot him in the head."
It was not clear Wednesday whether Marc Wabafiyebazu would be charged as a juvenile or an adult, AP reported. Authorities say he would not be protected by diplomatic immunity.
One witness said he heard multiple gunshots from inside the yellow apartment complex on a quiet residential street.
"(I heard) six straight shots," Alex Hernandez told the local ABC affiliate, and also told the local NBC station that he heard four more later outside the building.
"I saw some guy come out with a gun, some other guy behind him stumbling. He fell down, and some chick came out screaming."
Another neighbour said she panicked, entered her house and locked the door.
News footage showed a pool of blood in the doorway of the apartment complex, located just south of Miami's Little Havana.
The Canadian government says it's providing consular services, which it generally would when there's a death abroad — such as assistance with the repatriation of the body, and availability to attend court hearings if requested.
The boys' former school in Ottawa has put in place support services for students upset by news of the incident. They attended Lycee Claudel in Ottawa — a diplomatic school, with primary- and secondary-level students that runs on the French education system.
Both brothers attended the private school up until last year.
"Regardless of how many years they spent here with us, it's a story that really affects us. And to die so young — it's terrible. Obviously, we're thinking about their family," said the school principal, Pascale Garrec.
Wabafiyebazu last saw his sons in early February at a going-away party held for them before their move. He said he exchanged emails with them frequently in recent weeks.
"I don't know very many young people their age who wouldn't want to move to Miami," he said.
"It's sad that it turned out this way. They were very happy."
— With files from The Associated Press