The first of five people killed by a mass shooter in Philadelphia last week was most likely fatally shot about 44 hours before the others, authorities said Sunday.

The Philadelphia Police Department said in a statement that its investigation, with the help of the local medical examiner’s office, had determined that Joseph Wamah Jr., 31, was killed July 2.

On the evening of July 3, police say, the suspect in Wamah’s killing, Kimbrady Carriker, 40, opened fire indiscriminately in a neighborhood southwest of Center City.

Those killed in that incident were identified as Lashyd Merritt, 20; Dymir Stanton, 29; Ralph Moralis, 59; and Daujan Brown, 15. Boys ages 2 and 13 were injured, and other people were targeted but not struck, authorities said.

Authorities said the gunman was wearing a ski mask and a ballistic vest and carried an unmarked, unregistered ghost gun, multiple ammunition magazines and a semiautomatic rifle in the style of the AR-15.

The suspect, detained without bail, has been charged with five counts of murder, five counts of attempted murder, aggravated assault, possession of a weapon without a license and carrying firearms in public.

He was being represented by a public defender. The Defender Association of Philadelphia didn’t immediately respond to a request for comment on the latest statement from police.

Wamah wasn’t known as a victim until after the gunfire was over July 3. It wasn’t clear whether he and suspect knew each other; police believe the other victims were on streets and sidewalks and were shot randomly.

A senior law enforcement source briefed on the investigation said detectives believe Carriker is mentally ill. Philadelphia District Attorney Larry Krasner has said it’s likely his office will seek expert examinations of the defendant.

Police said Sunday that someone reported shots fired July 2 in the area of Wamah’s residence but that officers were dispatched to the wrong location, more than 3 miles to the north.

A caller to 911 reported gunfire in the area of 1600 S. 56th St. about 2 a.m., police said. Officers were dispatched to the 1600 block of North 56th Street and reported no evidence of a shooting, they said.

The matter is part of the investigation, police indicated.

In a statement Sunday, Krasner said, “The grieving family of the deceased has been briefed on this new information, and I cannot express enough the sorrow I feel.”

He praised police, however, for trying to get to the bottom of Wamah’s death.

“Law enforcement should always act with integrity and follow the facts wherever they lead,” he said.

Carriker is expected to return to court July 24.

Yasmeen Persaud and Tom Winter contributed.