MIAMI (CBSMiami.com) – Miami-Dade Police are pushing back against allegations officers over-reacted during a police shooting that left one man dead.

Miami-Dade Police said the man was wielding a knife and had no choice but to fire. The man's family disagrees.

"He was a good boy," Ana Bueno told CBS4's David Sutta about her nephew Manuel Buenos.

Ana is still having a hard time believing the officer fired in self defense.

"Why they kill him? I don't understand this. Why?" Bueno said.

According to investigators, Bueno came at the officer with a knife. Miami-Dade Police Officer Robert Williams explained, "He was in fear for his safety. This was deadly force being used against the officer. The officer had no choice but to respond."

Witnesses told a different story.

"The guy put his hands in the air and was still walking. The cop came from around the door with his gun and started shooting at the guy," a man at the scene told CBS4.

Even if Bueno was wielding a knife, family and friends believe the officer should have used his Taser.

"Some people think of the Taser as a cure-all. I can show you tapes of the Taser has not worked," Miami-Dade Officer Osvaldo Robles told CBS4 Tuesday morning.

Officer Osvaldo Robles trains Miami-Dade cops on how to defend themselves. The police department asked him to speak to the media in response to all the criticism from Friday's shooting.

He showed tapes of attacks depicting that a Taser sometimes cannot stop someone's forward movement and adrenaline. Robles explained once someone is on top of you with a knife it's too late.

"Let me ask you a question. Would you let me puncture you with a one inch blade on the neck?" he asked. The photographer in the audience responded, "No." Robles added, "Would you let me puncture you with a half-inch blade on your eye?" Again the photographer said, "No." Robles then shrugged as he made his point.

With a series of peaceful protests over the weekend, and more to come, the family is still not satisfied with the investigation thus far.

"I want justice. That's what I want. We want justice and answers. The police have to come and say why they did this injustice," Bueno said.