Still, FBI agents continued to scour Archer's Internet activity while attempting to retrace his steps on two recent trips to the Middle East - a month-long Muslim pilgrimage to Saudi Arabia known as the Hajj in fall 2011 and a 10-month stay in Egypt in 2012.
And investigators with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives were also working to determine how a police-issued firearm - a semiautomatic 9mm Glock pistol stolen from an officer's home in October 2013 - had made its way into Archer's hands as he fired 13 times Thursday into Hartnett's squad car at close range.
"They're trying to put together a puzzle," explained J.J. Klaver, a retired FBI agent who is not involved in the investigation. "They want to piece together did he communicate with anybody beforehand and determine how he came to these radical Islamic beliefs."
Hartnett, a Coast Guard veteran and an 18th District officer with four years on the force, continued to recover Saturday at Penn Presbyterian Medical Center, suffering from a broken arm and nerve damage.
Despite his injuries and heavy bleeding, he managed to shoot and wound his fleeing assailant. He was listed in critical but stable condition.
Meanwhile, Mayor Kenney, criticized in some corners Friday for attempting to divorce Archer's actions from the Islamic faith, stood by those earlier remarks Saturday during an appearance at a mural painting at the Al-Aqsa Islamic Society. The North Philadelphia mosque on Germantown Avenue was targeted by vandals who left a severed, bloody pig's head nearby last month, considered an act of defilement to Muslims who observe halal dietary laws.
"That act of that terrible man in almost assassinating our police officer was an individual act," Kenney told the mural gathering Saturday. "It was not an act of religion."
Questions lingered as to just how much Archer had in common with other U.S. Muslims who have recently carried out acts of violence inspired by - if not coordinated with - radical Islamic groups.
His trip in October 2011 to Saudi Arabia occurred during the Hajj, a pilgrimage to Mecca required at least once of all dutiful followers of the faith.
His 10-month stay in Egypt the next year overlapped with the beginnings of that country's uprising against then-President Mohammed Morsi - though FBI agents did not immediately link the events and continue to investigate the purpose of Archer's trip, special agent Eric Ruona said.
ISIS has specifically called on supporters worldwide to launch their own attacks on law enforcement officers and military personnel in recent months.
But Matthew Levitt, a terrorism expert at the Washington Institute and former FBI and Treasury Department analyst, said what role those calls might have played in Archer's attack is likely to remain hazy.
"All we can say is by January 2016, some combination of factors - almost certainly including some personal issues and some ideological concerns - combined to make him want to carry out this attack and claim he was doing it in the name of the Islamic State," he said.
Klaver, the retired agent, compared Archer to Syed Rizwan Farook and Tashfeen Malik, the California couple responsible for killing 14 people and wounding another 22 at a San Bernardino government building last month.
Archer's assault, he said, stood apart for its brazenness.
"In Philadelphia, this is the first time we've seen someone target police officers with apparent terrorist intentions," he said. "It's one thing to shoot innocent civilians who you presume are not trained or armed. It's another thing to walk up to a marked police car, when you know the officer inside has a gun and is trained to use it."
Hartnett, 33, was patrolling alone just after 11:30 p.m. Thursday near the intersection of 60th and Spruce Streets when Archer strode toward his cruiser, extended his arm, and opened fire.
A video of the shooting obtained by The Inquirer shows Archer - dressed in a loose white robe similar to the garment known as a dishdasha worn by Muslim men - leaning into the officer's squad car after pocking the vehicle with bullet holes. He opened fire again, turned, and sprinted back down the street.
Hartnett was hit three times in the arm. Bleeding heavily, his arm fractured and limp, he struggled out of his car and managed to run after Archer, fire back, and wound him.
Archer was arrested a block away - at 60th and Delancey Street - with a bullet wound to his buttocks and his gun lying next to him with the slide still locked. He had fired every bullet in the weapon, officers said.
Archer's mother, Valerie Holliday, said in an interview with The Inquirer on Friday that her son had "been acting kind of strange lately" and believed that police were targeting him. He had suffered head injuries from playing football and a motor scooter accident, she said.
She described him as a devout Muslim but said she did not believe he had been radicalized.
"He's been talking to himself . . . laughing and mumbling," Holliday said. "He's been hearing voices in his head. We asked him to get medical help."
Police, however, have described Archer as a man who knew what he was doing.
He repeatedly professed his allegiance to the Islamic State after his arrest and told investigators he attacked Hartnett because he felt police defended laws that were contrary to the Quran.
"I follow Allah," Archer told detectives, according to Homicide Capt. James Clark. "I pledge my allegiance to the Islamic State, and that's why I did what I did."
In recent years, Archer had been arrested in Delaware County and in Philadelphia and was on probation at the time of Thursday's shooting.
Before the attack, he had been scheduled for sentencing Monday in a 2014 case in Delaware County, where he was convicted of forging documents, careless driving, and driving with a suspended license.
As of late Saturday, Archer remained at the Curran-Fromhold Correctional Facility. In addition to the attempted-murder count, he faces charges including assault and reckless endangerment as well as gun violations.
Staff writers Aubrey Whelan and Stephan Salisbury contributed to this article.