After weeks of investigating who shot Armand Fennell during a botched robbery attempt and left him for dead on an Upper Darby street, police announced Thursday that a 21-year-old man had been arrested for the crime.

Deshawn Cannon, of Upper Darby, has been charged with fatally shooting Fennell in the back, with the bullet tearing through the 17-year-old's heart the night of July 7. Upper Darby police announced Cannon's apprehension at a news conference, where a paper print-out of Cannon's face was taped to the far wall. Cannon has been in Philadelphia Police custody since Aug. 15 on an unrelated charge of illegally owning a handgun, authorities said.

Deshawn Cannon, 21.
Katie Park / Staff
Deshawn Cannon, 21.

The relationship between Fennell and Cannon is unclear but authorities said they believe the motive in the crime was robbery.

Last month, less than 24 hours after he had been released from prison, police said Cannon was back on the streets of Upper Darby, where he headed to Glendale Road. A party attended by 40 to 50 people was in full swing, police said.

Fennell was also at the party, police said. At some point that night, police said Cannon tried to rob Fennell outside, but the teen turned and ran, and Cannon fired a fatal shot.

Witnesses were reluctant to speak to police following the fatal shooting, creating a "sluggish start" to the investigation, said Capt. David Madonna, commander of the Criminal Investigations Division at the Upper Darby Police Department.

"We were completely frustrated," he said.

Armand Fennell, 17, of Upper Darby.
Katie Park / Staff
Armand Fennell, 17, of Upper Darby.

Eventually, following pleas from Fennell's family and admonishment from township officials who said witnesses should step forward, tips began to trickle in through phone calls, social media, and in-person visits to police.

Madonna declined to say if authorities recovered the gun used in Fennell's killing.

"No death should ever come for a young youth being out in the community at night," said Upper Darby Mayor Tom Micozzie. . "… Unfortunately, in the society we see today with the leniency of our court systems, this gentleman is no stranger to the penal system."

Cannon has 2016 convictions for theft of a motor vehicle and public drunkenness. Court records show Cannon was sentenced to a maximum of 12 months in jail for the theft.

A picture of Fennell, an Upper Darby High School student who would have started his senior year this week, was also taped to the wall at police headquarters. The teen, who volunteered at the legislative office of Rep. Margo Davidson, D-164, had the nickname "Mando," Madonna said.

"I want to give extended condolences to the mom, who no longer has a son," Micozzie said.

Cannon is scheduled to be arraigned next week.