By Joe Holden

PHILADELPHIA (CBS) — On an early August morning in 2019, two men sitting on a street corner were ambushed and killed. The two men wanted for their murders, remain on the loose. In this week’s CBS3 Mysteries, police say they are in desperate need of the public’s help to get these killers off the street.

In previously unreleased surveillance video provided to CBS3 Mysteries from Philadelphia police, two men are seen walking down Cumberland Street. They’re about to wrap around the corner where 29-year-old Curtis Holmes and 21-year-old Tyrek Dunn are seated outside a convenience store.

CBS3 Mysteries: Police Need Help Identifying 2 Shooters In 2019 'Clear Assassination' Of Curtis Holmes, Tyrek Dunn

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It’s just before 3 a.m. on Aug. 18, 2019.

“They’re sitting on milk crates. They’re involved in conversation,” Philadelphia Police Capt. Jason Smith said. “We have these two individuals. They approach off Cumberland Street, our decedents are right on the corner. As soon as they turn the corner, they open fire.”

Both men are hit and rushed to the hospital. Neither one of them survives.

“We believe Mr. Holmes was the intended target and Mr. Dunn was just in the wrong place at the wrong time,” Smith said. “And he was collateral damage.”

Detectives say the man known as shooter No. 1 was heavily armed.

“Was a handgun with an extended magazine. The capability of that was probably 30 rounds,” Smith said.

Did they show up there looking to kill?

“Absolutely,” Smith said. “This was a clear assassination.”

Police have solid leads on shooter No. 1.

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They say an anonymous tip suggested he goes by the nickname “Jim Jim.” That’s something they’ve since confirmed as accurate.

The identity of shooter No. 2 remains a mystery.

But hampering their efforts is a wall of silence and lack of cooperation. Investigators say they’re running into a culture where people do not want to come forward.

CBS3 Mysteries: Police Need Help Identifying 2 Shooters In 2019 'Clear Assassination' Of Curtis Holmes, Tyrek Dunn

“This culture exists at the present time and it’s very sad because we know there are individuals who looked at video we gave to you, and they know at least who one of these shooters are, shooter No. 1 — the individual with the extended magazine,” Smith said.

Police know the hesitation to come forward is born out of the no snitch mentality and for fear of retaliation.

They see it “all the time,” Smith said.

“It makes most of these homicide investigations an uphill battle,” Smith said.

But investigators are hopeful that someone will speak up despite the real-life risks.

“Because of fear of their lives, they will not come forward,” Smith said. “We’re talking about the lives of two young men, brutally gunned down in Strawberry Mansion.”

If you have information on the two men responsible for gunning down Holmes and Dunn, call Philadelphia police at 215-686-8477.

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For a list of gun violence resources in Philadelphia, click here.