BROOKLYN (PIX11) — Carlos Collazo is furious over the Brooklyn District Attorney’s Office announcement on Monday that a grand jury declined to recommend criminal charges against Mark Smith.

Collazo told PIX11 News about his late son Isaiah Collazo, who was fatally stabbed on board a D train in Brooklyn a month after his 18th birthday.

That last night, I did – I dropped him off at the bus. I told him, ‘Be careful.’ That was the last I spoke to him,” said Collazo.

Smith is a 25-year-old male train passenger who police said fatally stabbed Isaiah.

“He didn’t deserve to get stabbed,” said Collazo.

Police told Carlos his son was with friends that night when one of them pulled the train’s emergency brake. That triggered an argument that turned into a physical fight with Smith.

Law enforcement sources familiar with this investigation told PIX11 News a witness who did not know either party stated the boys were the aggressors.

The grand jury ultimately found Smith acted in self-defense when he stabbed Isaiah and then ran off. Smith was picked up by police a few days later.

“And if it was self-defense, why did he leave?” asked Collazo.

“The facts of this case never inculpated Mr. Smith, and this outcome is consistent with his role in the incident and the law. The Brooklyn DA’s office conducted a thorough investigation, with Mr. Smith testifying directly to the grand jury, resulting in this just dismissal,” Smith’s attorney with the Legal Aid Society told PIX11 News.

The MTA is working to ensure detectives can rely on more than oral and witness testimony.

There are approximately 6,600 subway cars in the system. So far, more than 100 cameras have been installed under a pilot program, and the MTA is still actively procuring an additional 4,160 cameras.

The agency aims to have two discreet cameras in every subway car by 2025.

But for now, none of that can help Carlos Collazo.

“That one day he went out – he never came home. Over just like, some kid pulling a prank, and the guy saying he was defending himself,” said Collazo.