At a trial last month, prosecutors argued that Marcellus Jones, 34, of North Philadelphia, a convicted felon with a record of gun violence, feared that an accomplice would tell cops about their roles in the Zabel killing.
So, to silence him, Jones killed Tyreek Taylor, 20, in September 2008 with a single gunshot to the neck, they said, shooting him down in the street outside the rowhouse Taylor shared with his mother on the 1300 block of South Bouvier Street.
"The defendant's motive for killing Tyreek Taylor was to ensure that he would not or could not provide information to law enforcement regarding the investigation of the murder of Beau Zabel," according to a prosecution motion arguing that evidence in Zabel's death should be included at Taylor's trial.
A witness who knew Taylor and Jones testified that Jones had told him that he had killed Taylor to keep him quiet.
"He told me he had to do it," the witness said, according to court records. "Because Tyreek might be snitching on him for what they did to the teacher."
Though Jones has never been charged in Zabel's death, prosecutors were able to argue that his death was the motive in Taylor's killing by filing a "prior bad acts" motion, said Assistant District Attorney Deborah Nixon, who handled the Taylor case.
The strategy paid off when Jones was found guilty of killing Taylor. Common Pleas Court Judge Steven Geroff sentenced Jones to life in prison.
He was already serving 50 to 100 years for a March 2010 conviction for attempted murder in the shooting and wounding on June 2, 2008, of a South Philadelphia woman holding a baby in her arms on the 1600 block of Reed Street - a robbery committed just 13 days before Zabel was killed.
According to Pennsylvania law, courts will allow evidence of "prior bad acts" where the "crime or bad act" was part of a sequence of events that formed the case's "natural development of facts," she said.
Court rules impose a less difficult "burden of proof" when arguing bad acts.
Not wanting to go to prison for Zabel's killing, Jones "thought he could shoot his way out it," Nixon told the jury.
"He decided to be the judge, jury, and executioner," she said.
Zabel was thrilled at the chance to teach high school math in the public school system while earning his graduate degree from Drexel University as a Philadelphia teaching fellow.
He was filled with excitement and optimism for his new city and new life, his family and friends said.
Making his way home from work about 1:30 a.m. the night of his death, Zabel stopped to buy a can of Mountain Dew from a soda machine outside a fish and fruit stand at Eighth Street and Washington Avenue. Then he crossed Passyunk Avenue onto Ellsworth Street, out of range of the store's security camera.
Neighbors heard a loud boom, but thought it was a blown transformer.
Moments later, grainy surveillance footage showed a male wearing a white T-shirt and dark clothing running north on Eighth, away from Ellsworth.
The figure places something in a flower pot - perhaps the weapon or Zabel's iPod - before quickly returning to retrieve it.
Police pursued dozens of leads in the weeks after Zabel's death, reviewing other cases of gunpoint robberies in the area, including the May 2008 robbery of a woman near Seventh and Federal Streets, according to the court documents.
A white Samsung phone stolen during the robbery of the women led police to Taylor.
In an interview with Homicide Detective George Fetters and Officer Chris Lai, Taylor denied knowing anything about the robbery of the woman or the death of Zabel, according to court records.
He told police he bought the phone from a "smoker" he knew only by the nickname of "Ant North" - who police would later learn was Jones.
With his refusing to cooperate further - and with no evidence against him - police released Taylor.
About 10:30 a.m. Sept. 6, 2008, Taylor parked his black Pontiac near his mother's house on Bouvier Street in South Philadelphia.
Jones was waiting for him, lying in wait inside an abandoned house.
Witnesses said they saw Jones come up behind Taylor, shoot him once in the neck, then search through his car and pockets.
Police later found Jones' DNA on a menthol cigarette inside the abandoned house.
In November 2009, police received a letter from a man who knew both Taylor and Jones.
The witness, who was in prison at the time, told police that in the hours after Zabel's death, he received phone calls on an illegal prison cell phone from a panicked Taylor.
Taylor was trying to get in touch with his older brother, the witness said.
The witness said Taylor and Jones were known to commit robberies in South Philadelphia.
On the phone the night of the murder, the witness said, Taylor told him he had been with Ant North and that "Ant North did some dumbass s-," according to court records.
The next day, according to the records, the witness said Taylor and his brother told him that the two men had been out in South Philly on the "prowl for a victim to rob" and that Ant North "rocked him" because he didn't have anything.
A few months after the Taylor killing, the witness talked with Jones in a prison cafeteria.
"He told me Tyreek was weak," the witness said. "He thought he was snitching that he killed that teacher."
Police say Jones' conviction - and life sentence in the Taylor killing - will not deter them from investigating the Zabel killing.
Rather, they hope that, with Jones off the street, other witnesses could step forward and provide them with the "final link" in the case, said Lt. Mark Deegan of homicide's Special Investigations Unit. He is supervising the Zabel case, assisted by Detectives Fetters and Jack McDermott.
"We want to be able to call his parents and say, 'We've arrested the man who we believe killed your son,' " Deegan said. "This is a kid who came here to help, who was going to contribute. He picked us. He wanted to help us. And the last time I checked, we don't get a lot of those folks."
Zabel's mother, Lana Hollerud, and stepfather Terry Zabel flew in from Minnesota to watch Jones be tried in Taylor's death.
It saddened Hollerud that another mother had felt the pain of losing a child, she said. After the closing arguments, she hugged Taylor's mother and told her she hoped a guilty verdict would bring some relief.
Hollerud said she took comfort from the hard work of the detectives in pursuing justice in Taylor's and her son's deaths.
"Even after four years," she said, "it was comforting to know that Beau had not been forgotten."
Anyone with information about Zabel's death may contact police at 215-683-3334.
Contact Mike Newall at 215-854-2759 or firstname.lastname@example.org.