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EXCLUSIVE DETAILS – The Virginia physician assistant accused of stalking his ex-girlfriend for three days before murdering and mutilating her husband in New York had been in a years-long relationship with the woman before they split about four years ago, Fox News has learned. 

"I promise you, there will be more charges coming."

— Albany County Sheriff Craig D. Apple Sr. to Fox News Digital 

Jacob L. Klein and the 29-year-old woman had been in contact via written communication at some time over the past year, but had not seen each other in three to four years, Albany County Sheriff Craig Apple told Fox News Digital. But last week, he drove to New York and began stalking the woman and her 35-year-old husband, physician assistant Philip Rabadi, for three days before unleashing his violent attack, officials have said. 

VIRGINIA PHYSICIAN ASSISTANT STALKS EX-GIRLFRIEND FOR 3 DAYS BEFORE MURDERING, MUTILATING HER HUSBAND

Virginia physician assistant accused of stalking his ex-girlfriend for three days before murdering and mutilating her husband in New York

Left: Photo from victim Ellie Radin's Facebook page shows Radin and her husband, Philip Rabadi. Right: Booking photo for Philip Klein (Albany County Sheriff's Office) (Facebook; Albany County Sheriff's Office)

The 40-year-old then allegedly fatally stabbed Rabadi at the couple’s Albany-area home on the morning of April 13, after Rabadi’s wife had already left for work. 

Officers and family members conducted a welfare check at the home on the morning of April 13 after Rabadi never showed up for work. They discovered Rabadi lying dead on the floor of the garage, with "his arms bound with multiple stab wounds and mutilation to his body," police have said. 

Speaking over the phone on Tuesday, Apple could not speak to any threats or threatening comments Klein might have made to the woman or the couple. He said investigators executed search warrants at Klein’s Virginia home, where they commandeered computers that they would be examining for any evidence in the coming weeks. 

Investigators executed more than 11 search warrants and six subpoenas in the first 48 hours of the case alone, police said. 

Apple said Rabadi had never met Klein but likely knew of him. 

Klein, Rabadi and his wife, identified on social media as Ellie Radin, were physician assistants, according to multiple reports, and the couple worked at the same New York hospital. 

Klein is not married and does not have any children, Apple said. He noted that Klein had legally purchased the guns he was found to have been in possession of, and bought them in his home state Virginia

On Tuesday, the sheriff described how camera footage from the area shows Rabadi exiting his home to speak to someone, whom investigators believe is Klein, on the morning of the attack.

"And they communicate a little bit. Some of it, you can see, is very non-confrontational," Apple told Fox News Digital by phone. 

But things then appeared to take a turn. 

"At some point in the conversation, something is said that causes Mr. Rabadi to just basically kind of turn around slowly and walk in the house with this individual … following him in and the door closes," Apple continued. 

The Times Union previously reported that Rabadi appeared in the video to be reacting to what looked like some sort weapon. When asked about this detail on Tuesday, Apple responded, "That’s a fair statement."

He would not say whether it appeared the weapon was a firearm or something different. 

Klein was arrested in Virginia late Friday on a federal charge of unlawful flight from prosecution. 

Apple said police recovered a handgun from the vehicle Klein was driving when he was arrested. Klein reportedly has no prior criminal history and is a U.S. military veteran who has also lived in California and New York.

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He was arraigned in Virginia District Court on Tuesday afternoon, when he waived extradition, according to WJHL-TV

He will soon be extradited back to New York, where the Albany County Sheriff’s Office charged him with second-degree murder. 

Apple told Fox News Digital that his office charged Klein with murder as quickly as they could because it was the most serious crime to which the man has been linked. Doing so, Apple said, created the "path of least resistance" to get Klein into custody and out of harm’s way for the public and himself. 

"We wanted to get him in custody. I didn't want him out, you know, able to hurt someone else. I didn't want [him] to hurt a police officer who was trying to stop him. And I certainly didn't want him to hurt himself, either," Apple said. "The murder-second was the initial charge. I promise you, there will be more charges coming."

Apple would not provide details regarding the evidence of Klein’s alleged harassment, citing the ongoing investigation.

Radin thanked the public for their support in a Facebook post on Wednesday. 

"I know an endless amount of love and strength is being sent my way,"she wrote. "These words do not come close to completely encompassing Phil, but they are mine and I'd like to share them."

An obituary published Tuesday for Rabadi described the Rabadi and his wife as being "true soulmates and partners in life."

"Philip’s legacy will never be forgotten," the obituary further states. "He made the lives of those around him better. He made the world better."

It added: "He will be remembered by his friends and family when they hear a Dave Matthews song, have an ice cream, sip a great IPA, hit a PR in the gym, land a joke for a crowd, walk the halls of St. Peter’s, watch Liverpool score a goal, nail a golf swing, let loose on a dance floor, or drink their morning coffee."

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The family has since created The Philip L. Rabadi, MS, PA-C '15 Legacy Fund at Albany Medical College in his honor.

Services have been scheduled for Wednesday and Thursday at the Albany Country Club.