A building handyman was convicted Monday of fatally stabbing retired Villanova University professor Carol Ambruster during a 2013 robbery in her Germantown apartment.

Jurors deliberated just 30 minutes before returning guilty verdicts on first-degree murder, robbery, and related offenses against Jose Diaz, also of Germantown. When the foreman read the verdicts, the victim’s sister, Ariel, softly wept.

Shortly afterward, Common Pleas Court Judge J. Scott O’Keefe sentenced Diaz, 48, to the mandatory term of life in prison without parole for the murder. Diaz, a thin man with shoulder-length gray hair, showed no reaction when the verdicts were read and declined to say anything during sentencing.

O’Keefe, who read letters submitted by Ambruster’s loved ones, told Diaz: “This is a wonderful, compassionate person whose life you snuffed out.... It is despicable and horrendous.”

The jury’s decision came after a weeklong trial at the Stout Center for Criminal Justice in which a prosecutor argued the evidence against the defendant was “overwhelming.”

“He walked through her blood and tried to clean it off,” Assistant District Attorney Jason Grenell told jurors in closing arguments Monday morning. But, the prosecutor said, police investigators found that the size and tread markings of bloody boot prints from Ambruster’s apartment hallway matched a pair of size 8 Timberland boots found in Diaz’s home.

The boots appeared to have been cleaned up, but tests showed that DNA from Ambruster’s blood was on Diaz’s boots, Grenell said.

Defense attorney Gina Amoriello had contended that Ambruster’s roommate, Daniel Sapon, killed the retired astronomy professor, a claim the jury rejected.

The evidence showed that Diaz, who had access to the apartment building at 5501 Wayne Ave., surprised Ambruster, 69, after she returned to her apartment about 6 p.m. Dec. 9, 2013, and repeatedly beat and stabbed her with a knife from her kitchen. In his last act, he shoved the knife into her throat and left it there, Grenell said.

As the prosecutor described the last stabbing, the victim’s sister, sitting in the second row of the gallery, covered her face with her hands.

During his closing statement, Grenell also pointed to investigators’ discovery of Diaz’s bloody fingerprint on the back of Ambruster’s belt. Authorities believe Diaz held onto the belt as he dragged her body from the hallway into the pantry, then into her kitchen. Grenell again showed jurors the bloody scene in Ambruster’s second-floor apartment — her dried blood in the front hallway and the bloody smear marks on the floor.

He reminded jurors of testimony last week by Diaz’s then-wife, Angela Enoch Diaz, who testified that Diaz wasn’t home when she returned to their Germantown home about 6 p.m., around the time Ambruster was killed, and didn’t return home until the next afternoon.

Both the prosecutor and defense attorney agreed that Diaz had a drug problem. Grenell contended that Diaz needed money for drugs and that’s why he tried to rob Ambruster in her apartment. Whether he actually got away with any money is unclear, Grenell said. Ambruster’s pocketbook, with its contents strewn about, was found by her feet on the kitchen floor.

Amoriello, during her closing argument Monday, said she couldn’t explain how Diaz’s fingerprint got on the victim’s belt.

Last week, Grenell had introduced surveillance video from inside the Essene Market in Queen Village, showing jurors that Sapon was inside the store at 6:30 that night, around the time Ambruster was killed. Sapon found Ambruster’s body when he returned to their apartment later that night.

During Monday’s closing arguments, Grenell pointed to Sapon, who was sitting in the gallery, and said of the defense’s claims: “I’m sorry he has to sit through these allegations of being some type of murderer.”

Ariel Ambruster, of California, was accompanied at the trial by two of her sister’s close friends, Frankie Grace of Alaska and Beth Jewell, a former assistant in Villanova’s astronomy department. Jewell thanked the Crime Scene Unit and other police officers for their investigation in figuring out who killed Ambruster.

“Finally, for us, it’s over,” Ariel Ambruster said.

Her sister earned a doctorate in astronomy from the University of Pennsylvania in 1984, and taught at Villanova from 1987 to 2011. She recalled how her sister loved collecting glass bottles in West Philadelphia, where she lived when she attended Penn.

“Carol loved Philly,” she said.