A suspect held on suspicion of killing five people in a shooting where pedestrians and vehicles were fired at in southwestern Philadelphia on Monday night is scheduled to be arraigned Wednesday on murder charges, a district attorney said.

The 40-year-old suspect, who had not been named publicly as of Tuesday night, also is expected to face aggravated assault, weapons charges and other accusations, Larry Krasner, the Philadelphia district attorney, said during a news conference Tuesday.

The suspect, whom prosecutors are referring to using they/them pronouns, had not been charged as of Tuesday night.

Authorities say the suspect appeared to fire randomly on several blocks of southwest Philadelphia's Kingsessing neighborhood Monday night before officers arrested that person during a chase on foot. The suspect had an AR-style rifle, a 9 mm handgun and a scanner that tracks emergency response radio traffic, and was wearing a bulletproof vest and a ski mask, authorities said.

"We believe it appears this individual acted alone," Philadelphia police Staff Inspector Ernest Ransom said Tuesday.

Killed in the shooting were Daujan Brown, 15; Lashyd Merritt, 20; Dymir Stanton, 29; Ralph Moralis, 59; and Joseph Wamah Jr., 31, police said. Wamah's body was found in a home early Tuesday, while the others were found Monday night, authorities said.

Two boys, ages 2 and 13, were shot in their legs and were in stable condition, police said. Also, a 33-year-old woman and another 2-year-old boy were injured by glass, authorities said.

The two 2-year-old children are twins who were in a vehicle that was fired at, authorities indicated at a news conference Tuesday.

The Philadelphia district attorney's office is using they/them pronouns to refer to the suspect based on "information we have at this time," a spokesperson for the office told CNN. Philadelphia officials previously used he/him pronouns for the suspect during a Tuesday news conference.

The shooting was one of more than 345 mass shootings that have unfolded across the US so far this year, according to the according to the Gun Violence Archive. CNN and the archive define a mass shooting as one in which four or more people are shot, not including the shooter.

Monday's shooting in Philadelphia came during a holiday period filled with deadly gun violence. That included a Monday night shooting in Fort Worth, Texas, where at least three people died and eight were wounded. The day before, two people were killed and 28 were injured in a shooting in Baltimore.

Tuesday marked one year since a shooting at a July Fourth parade in the Chicago suburb of Highland Park killed seven people and wounded others.

Sprawling crime scene spanned several blocks

Police learned of the shooting around 8:30 p.m. Monday when officers were flagged to the crime scene and found multiple people with gunshot wounds, Philadelphia Police Commissioner Danielle M. Outlaw said.

"As they were scooping up victims and preparing them for transport to the hospital, they also heard multiple gunshots up the street," Outlaw said.

After responding to the second shooting site, officers again heard more gunshots on a nearby street, she said.

Investigators believe Wamah, the victim who was found dead in a home, was the first person killed in the shooting Monday night, authorities said Tuesday.

Wamah's father found his body in a living room around 12:30 a.m. Tuesday, city police Chief Inspector Scott Small said.

Wamah had been shot several times, and responding medics declared him dead shortly after, Small said.