A British scientist who reportedly was visiting his girlfriend in the Atlanta area has been killed by a stray bullet in an incident that police are describing as a "random act." 

Investigators in Brookhaven were "following up on all leads" Monday afternoon following the death of Matthew Willson on Jan. 16, Sgt. Jake Kissel told Fox News Digital. The 31-year-old astrophysicist was shot inside an apartment shortly after arriving to visit his girlfriend Katherine Shepard, whom he met while studying at Georgia State University, according to the Atlanta Journal-Constitution.  

"The smallest thing we could ask for is that whoever did [this] is held accountable," Shepard told the newspaper. 

Matthew Willson, left, was visiting his girlfriend Katherine Shepard, right, in the Atlanta area at the time of the shooting, reports say.

Matthew Willson, left, was visiting his girlfriend Katherine Shepard, right, in the Atlanta area at the time of the shooting, reports say. (Courtesy Brookhaven Police Department)

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As of Monday, police have not announced the identities of any suspects in the case. 

"This incident appears to be a random act involving individuals participating in the reckless discharge of firearm(s) which led to the tragic death of Dr. Willson," Brookhaven Police said in a statement. 

The Atlanta Journal-Constitution, citing police, reported that the bullet that struck Willson in the head is believed to have been fired from a nearby apartment complex around 2 a.m. that Sunday before sailing into Shepard’s bedroom, where he had been staying. 

Police said they received multiple 911 calls reporting shots being fired in a complex in the 3600 block of Buford Highway, while a separate caller said a man – later identified as Willson – was struck inside a building along the 3100 block of Clairmont Road. 

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"He woke up to gunshots," Shepard told the newspaper. "I heard them and I had just turned off the light." 

"Then the bullet came through," she continued. "Then I heard his breathing change." 

Willson – who lives in England -- ultimately was pronounced dead at a local hospital. 

"He was so happy to be here and be able to spend time with Katherine," his sister, Kate, told the Atlanta Journal-Constitution. "It’s impossible to comprehend how it is even true." 

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The University of Exeter in southwest England, where Willson once studied as a doctoral student, described him as a "much-loved member of our astrophysics team," according to the BBC

"Our hearts go out to his family, friends and colleagues," the school added. "We are offering support to colleagues at the university who will also want to commemorate his life."