A nearly seven-hour standoff in Butler ended peacefully this morning when police took into custody four males holed up in an apartment of a house in the 400 block of Franklin Street, authorities said.

Investigators were still trying to sort out what led to the standoff that initially came in as a possible armed robbery.

“The investigation is just beginning and there are a lot of questions,” Butler police Deputy Chief David Adam said shortly after 4:30 a.m. “We're still trying to piece things together.”

The drama began to unfold just after 9 p.m. when a resident called 911 to report a break-in at the apartment.

The 911 caller said, “There's a man with a gun in my house,'” Adam said.

The 911 caller lives in the multi-story house that is divided into at least four apartments.

Authorities did not immediately identify the 911 caller, who Adam admitted is known to police. He said he could not elaborate.

City officers got there and saw a black male coming out of a second-story window. He appeared to have a handgun.

“Police announced their presence and he jumped back in,” Adam said of the suspect.

Butler Township police and state police were called in to assist for the possibly armed conflict. While police surrounded the house, they also tried to make sure all the other tenants were safe.

Officers knocked on doors and windows of the other apartments. By then, however, most of the occupants had already gotten outside.

It was also learned that the 911 caller, too, was safe.

The caller “may have come running out at some point,” Adam said, “we don't know.”

Before long, police requested the help of the Allegheny County SWAT team, which took over the operation.

The specially-trained officers dressed in camouflage and Kevlar helmets and carrying high-powered rifles and ballistic shields spread out throughout the neighborhood.

“It was scary to watch,” said Rachel Barnes, who lives with her husband and their young child across the street. “We were saying prayers that no one gets hurt.”

Police soon learned that there was more than just one person barricaded inside.

“From the intel we had,” Adam said, “we knew there were at least three, maybe four.”

SWAT officers by loudspeaker tried to make contact with the suspects but to no avail.

“They were saying, 'This is the police. We have you surrounded. Come out with your hands up and stay away from the windows,'” said Barnes.

The speaker blared the same message periodically until at least midnight.

Butler police, meanwhile, contacted the owner of the house.

“Once we talked to the landlord,” Adam said, “we got the layout of the house. We found out that the whole house was accessible through the basement and attic.”

The decision was ultimately made to go in shorlty before 4 a.m., authorities said. But first, investigators obtained a search warrant.

Officers fired exploding tear gas canisters through the second-floor windows and apparently forced their way through at least one door.

“There were no (gun) shots fired, that I'm aware of,” Adam said. The four suspects were detained and taken to the station for questioning. No charges were immediately filed.

The 911 caller told police that they did not know any of the four males.

Police did not immediately recover any guns. But a more thorough search was to follow.