Nine people, including children, died in a mass murder on Friday in Erie, Pennsylvania, after a gun-wielding attacker opened fire outside a home and then entered the property, according to authorities.

The suspected attacker was also found dead as police responded to the deadly violence, which triggered a standoff involving Erie police officers and tactical teams.

Police discovered the killings at about 5pm when officers were called to a residence following reports of gunfire. Witnesses told authorities that they had seen an attacker with a gun outside the property before making his way inside.

Responding officers discovered two women lying dead in the street, both having suffered fatal gunshot wounds.

The situation quickly developed into a standoff as police officers and tactical personnel surrounded the residence. More gunshots were heard coming from inside the home, and officers entered the place.

Inside, police said they made a devastating discovery, finding seven additional victims, including children, along with the suspected attacker. Investigators believe the attacker died from a self-inflicted gunshot wound.

Erie’s police chief, Rick Lorah, spoke about the scale of the mass murder, describing the scene as among the most distressing and heartbreaking he had witnessed.

“The loss of life is devastating and the circumstances we are working through are deeply disturbing,” Lorah said. “At this time, we can confirm that the suspect is deceased. Based on the information currently available to us, there is no ongoing threat to the public.”

He added: “Our hearts are with the victims, their families and everyone affected by this tragedy. There are no words that can adequately express the magnitude of the loss of life here.”

Authorities on Saturday said they were still investigating the circumstances surrounding the killings, with authorities attempting to determine a motive for the violence.

The city of Erie also issued a statement on social media confirming that the suspected shooter had died and that the immediate danger had passed.

The statement described the case as a “terrible tragedy”, although the city’s statement did not provide further information about the events leading up to the shooting.

“We understand that the news brings deep shock and sorrow to our residents, and we want to assure the public that the situation has been contained,” the city said.

Figures from the Gun Violence Archive indicate that the killings in Erie marked at least the 19th mass murder of the year. Such cases are defined as ones in which four or more victims are murdered.

Many of those mass murders have been what are considered family annihilations, in which an attacker kills multiple close family members.

The nonpartisan archive also indicated that the killings in Erie were among more than 500 mass shootings across the US since the beginning of January. Mass shootings are defined as cases in which four or more victims are shot whether fatally or non-fatally.

Mass shootings for years have remained a persistent problem in the US, often intensifying public demands for stronger gun control measures at the federal level.

Despite those calls, Congress has not enacted such restrictions sought over the years.