After seven years investigating what was long considered a cold case, the trial of the South Philadelphia man accused of killing Minnesota teaching student Beau Zabel for his iPod opened Tuesday before a Philadelphia jury.

Assistant District Attorney Tracie Gaydos told the Common Pleas Court jury in her opening statement that dogged detective work and Marcellus Jones' indiscreet admissions to friends and relatives would prove that he shot Zabel, 23, in the back of the neck early on June 15, 2008.

Richard J. Giuliani, the lawyer representing Jones, 37, acknowledged that defending his client would not be easy, especially given Jones' 2012 murder conviction for shooting Tyrek Taylor, 19, of South Philadelphia, the man prosecutors say drove the getaway car for Jones the night Zabel was killed.

Gaydos said witnesses would testify that Jones told them he killed Taylor because he was talking about Jones' "killing the teacher."

Giuliani, however, told the jury of 10 women and two men that it would not hear "one bit of physical evidence linking this case to this man."

Instead, the prosecution case is built from statements incriminating Jones, made years after the fact, from people desperate to earn favorable treatment from prosecutors and escape long prison terms, he said.

Mostly, Giuliani urged the jury not to be swayed by sympathy for Zabel and the bright future that will never be.

The defense attorney called Zabel's slaying "a black mark on the city," and said detectives were under great pressure to come up with an arrest.

"This is not going to be easy, but you can do it," Giuliani told the jury. "I'm going to ask you to do the right thing, not the easy thing."

The jury returns to court Wednesday for the beginning of testimony presented by Gaydos and fellow prosecutor Jacqueline Juliano Coelho.

Tuesday's court session was taken up by selection of the 12-member jury plus two alternates, followed by the opening statements.

Zabel was a teaching fellow enrolled at Drexel University, where, in October 2008, he planned to teach during the day and take evening courses toward his certificate.

In the interim, Zabel got a job at a Starbucks store on South Street. Zabel had lived in Philadelphia for just six weeks when he was shot and killed as he walked home around 1 a.m. after finishing his shift.

Gaydos said Zabel was walking on the 800 block of Ellsworth Street with earbuds in, listening to his iPod, when he was shot from behind. When the shooter left, he took the iPod.

Although the shooting was witnessed by two women who lived on Ellsworth, no one has identified Jones as the shooter. No DNA or other physical evidence was found linking Jones to Zabel's body.

Zabel's parents, Lana Hollerud and Terry Zabel, and other family members traveled from Minnesota to be present for the trial.

Jones, who had no one among the spectators, had tried to represent himself.

On Tuesday, with the jury out of the room, Jones several times interrupted Giuliani to protest what he said were rulings by Judge Rose Marie DeFino-Nastasi preventing him from producing evidence from cellphone calls that he said would show he was not at the murder scene.

When the judge questioned Giuliani, however, he said he had no such evidence.

215-854-2985@joeslobo