Navek shot himself and died later at Virtua's new 368-bed, 680,000-square-foot regional medical center, which is nearby.
He was a Williamstown resident who grew up in South Philadelphia before moving away in his 20s, according to a former neighbor in the city.
Houshmandpour was a resident who worked at various Virtua locations on medical/surgical rotations, the hospital said in a statement.
"Before he could actually enjoy this life, his life was taken from him," the victim's sister, Parisa Houshmandpour, 28, said from Greensboro, N.C. "I'm still in shock."
Payman Houshmandpour and Navek knew each other through work. Hospital officials said Navek left a year and a half ago, but wouldn't comment on the reason.
Authorities said Wednesday that they believed the two men had a running dispute but did not disclose the nature of it.
The mother of Navek's longtime girlfriend told the Associated Press that Navek blamed Houshmandpour for what she said was his dismissal from the program at Virtua.
Forogh Mozaffari said her daughter recently broke up with Navek.
A neighbor of Navek's in the The Arbours in Williamstown said Navek's girlfriend moved out of the house about a month ago amid a police presence. Speaking on condition of anonymity, he said the couple were parents of a toddler.
Monroe Township police said they had been called twice to the house in the last month. They would not provide details.
Mozaffari said that after leaving Virtua, Navek served in the Army Reserve in Georgia and then North Carolina. The Army Reserve confirmed he worked as a medical doctor.
Navek's former neighbor in Philadelphia recalled that he once worked as an EMT there.
Houshmandpour came to the United States as a youth with his parents and sister after the family, which is of the Baha'i Faith, fled religious persecution in Iran and spent time in Pakistan.
"My parents wanted me and my brother to get an education," said Parisa Houshmandpour, who recently took the bar exam. "My parents sacrificed everything for us to be here. . . . We were just finally about to make it."
She said her brother graduated first from the University of North Carolina at Greensboro and then from medical school in St. Kitts and Nevis, in the Caribbean. He was a couple of months away from completing his residency and was mulling a job offer in South Carolina, she said.
Navek was stopped by police based on a witness' description of his car. Officers ordered him to raise his hands as they approached. He instead fatally shot himself.
The murder and suicide stunned residents in Voorhees' Main Street area, home to many health-care professionals.
"I heard boom, boom, boom, boom, boom," said Bob Williams, a retired 67-year-old corrections administrator who lives nearby. "I knew it was gunshots. It's truly unfortunate."
Another resident in the development, Dave Taylor, a doctor at Hahnemann University Hospital in Philadelphia, said he and his wife were sleeping when he heard loud noises outside. But he did not recognize them as gunshots.
"You think someone dropped something upstairs," he said. "I just rolled over.
"This is a quiet development with a number of fairly young professionals," he said. "It was kind of surreal seeing video of my apartment complex from a helicopter [on the TV news]. The shooting took place four cars away from my car. I'm glad I wasn't out there."
Taylor said he often saw Houshmandpour and his family at the pool and in the complex. "They were quite pleasant neighbors and would wave," he said. "He would come and go at odd hours. We're both doctors."
Virtua extended condolences to the families of both Houshmandpour and Navek "during this very tragic situation."
"At this time we are working closely with our staff to address their concerns and also to meet the needs of our patients," Virtua said in its statement.
On Wednesday afternoon, Parisa Houshmandpour was trying to make sense of what happened.
"All he did was save people's lives and they just took his life for no reason," she said of her brother.
The Associated Press contributed to this article.
Contact staff writer Edward Colimore at 856-779-3833 or firstname.lastname@example.org.