A 21-year-old University of Mississippi student who a friend claimed was "harassed" by her alleged killer "for years" died of "multiple gunshot wounds," according to a preliminary autopsy report released Wednesday.

The Lafayette County Sheriff's Department announced the result of the report Wednesday and formally ruled Kostial's death a homicide.

Fellow Ole Miss student Brandon Theesfeld, 22, was arrested Monday and has been charged with Kostial's murder. Authorities said Theesfeld was taken into custody at a gas station in Tennessee. Law enforcement officials told Fox 13 Memphis that Theesfeld was found with clothing that appeared to have blood on it.

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Kostial was found dead late Saturday near a lake in Harmontown, about 30 miles from the Ole Miss campus in Oxford.

On Tuesday a woman who said Kostial was her “best friend” tweeted of Theesfeld: "He harassed her for years, took advantage of her for years, I spent countless nights holding Ally close drying her tears about this monster for years.”

"You deserve hell you disgusting excuse for a human being," the woman added." ... You will never diminish her sunshine".

Tony Farese, a lawyer who is representing Theesfeld, said he and another Mississippi attorney, Steve Farese Sr., were retained on Wednesday. He declined to respond specifically to the harassment claims against his client.

"We are in the process of investigating the events surrounding the allegations against our client," Farese said in an emailed statement to Fox News. "It is far too early to make further comments on this matter."

Theesfeld's father, Daniel Theesfeld, said in a statement to WMC-TV that his son “is innocent.”

“I have reasons to believe that. I can’t share anything now,” he added.

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Kostial was last seen stopping at the door of a bar in Oxford Friday night but apparently did not go inside. Instead, officials told WLBT-TV that the 21-year-old went home around midnight before apparently leaving the house again, unbeknownst to her roommates.

It's unclear how Kostial got from Oxford to Harmontown.

The University of Mississippi confirmed to Fox News on Tuesday that Theesfeld was a student in the School of Business Administration, and has been suspended. Fox News also has learned Theesfeld participated in the Junior Reserve Officers' Training Corps program at San Marcos Academy in Texas. He graduated from the college prep academy before heading to Ole Miss, where he studied marketing.

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Kostial was working towards a bachelor's degree in marketing. Her father, Keith Kostial, posted on Facebook that his daughter had been attending summer school and teaching fitness classes at the university.

Fox News' Travis Fedschun, Andrew Keiper, Kimberly Wagner and Charles Watson and The Associated Press contributed to this report.