HAD THE trigger been pulled in another section of North Philadelphia's sprawling 35th Police District, there's a chance the deluge of shots - bang bang bang bang bang - might have gone unnoticed, or at least unreported.

But the gunfire echoed across a long, leafy driveway in the wee hours on Colonial Street, a winding block of tidy rowhouses in West Oak Lane, just a stone's throw from the Cheltenham Township border.

The terrifying noise awoke residents on Aug. 19. They didn't hesitate to call 9-1-1.

Some said they sighed in relief when they peeked through curtains and saw uniformed cops patting down three men, all of whom, law-enforcement sources have told the Daily News, were armed.

But then a strange thing happened. A supervisor from the 35th District, Sgt. Shaun Butts, arrived at the scene.

After a brief discussion, Butts allegedly told the other cops to let the three men go, the sources said.

Their weapons weren't confiscated. The men weren't taken in for questioning, nor was any information about them entered into police records, sources said.

At least 17 fired cartridge casings were left untouched on the ground in the driveway, behind a corner rowhouse that sported a broken window.

And that was that - until the next day, when a cop who felt uneasy about the whole episode contacted Internal Affairs, the sources said.

Internal Affairs is now investigating the incident. Butts, a 19-year veteran of the force, is on desk duty, and has been stripped of his police-issued firearm.

When reached by phone on Friday, Butts, 41, said he couldn't discuss the case because of the open investigation.

But then he added: "The allegations made against me are not true."

Butts serves as the treasurer for the Guardian Civic League, an organization that champions the rights of black police officers.

The organization's president, Rochelle Bilal, lives on Colonial Street, where the shooting occurred.

Crime Scene Unit investigators visited Colonial Street two days after the shooting and collected the cartridge casings, which were still sitting in the driveway, the sources said.

Internal Affairs investigators went door-to-door, asking residents what they saw and heard.

The shooting was still a topic of concern around dinnertime one night last week.

Little kids played on the sidewalk as the block started to fill with the sounds of people returning home from work - car doors slamming, keys jangling and mailboxes creaking open.

"Why did they let them go?" one resident, who didn't want to be named because she feared retaliation, asked of the men who were questioned at the scene.

"I called 9-1-1 two times that night," she said. "I was asleep at the foot of my bed, and the sound woke me up. It sounded like an Uzi. It was that bad."

Sources said it appears that a .22-caliber handgun was used to fire some of the shots.

"We have never had any problems like this,"said block captain Essie Holmes, who's lived in the neighborhood for 27 years.

"Everybody is still trying to find out what happened."

Holmes said that Capt. Joseph Fredricksdorf, the 35th District's commander, met with some residents about a week after the shooting and assured them that the incident was being investigated.

Fredricksdorf made no mention of the three men who were stopped and let go, however, or of the Internal Affairs probe into Butts, Holmes said.

Neither Fredricksdorf nor Police Commissioner Charles Ramsey responded to a request for comment.

Meanwhile, Bilal said that she was home the night of the shooting, but didn't hear the gunshots.

"I didn't find out anything until I saw officers down at the other end of the street," she said. "I came out and saw police cars there."

She agreed that shootings are unusual in her neighborhood but "that's starting to change,"she said, blaming troublesome tenants of a nearby apartment building.

She also defended Butts: "I know Sgt. Butts, and I don't think he deliberately did anything inappropriate. . . . I don't know exactly what happened. I'll let Internal Affairs do their job."

This isn't the first time Butts has found himself in the middle of controversy.

He filed a lawsuit against the city and the Police Department last year, claiming that he faced racial discrimination and retaliation for being part of a 2009 lawsuit that the Guardian Civic League filed against the city over Domelights, a sometimes vile online message board that was regularly used by cops to spread gossip.

Butts claimed in his lawsuit that he faced difficulties at work for speaking out about Domelights, and was passed over by Ramsey for a promotion and also suspended for five days for granting vacation time to a handful of cops - after his boss had told him not to.

He had also been suspended for three days after his police-issued firearm was stolen in 2011.

-Staff writer Dana DiFilippo contributed to this report.

On Twitter: @dgambacorta