ATLANTA -- A chance encounter in the lobby of a luxury midtown Atlanta condo building led to the death of prominent cancer researcher, according to homicide investigators.

Police arrested Shamal Thompson, 27, Thursday morning, charging him with killing Dr. Eugenia Calle, 57, in her penthouse apartment at the Aqua Midtown building on 10th Street at West Peachtree Street Tuesday.

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Investigators told WSB-TV Channel 2 reporter Lori Geary that Thompson was in the lobby of the building with a real estate agent when Calle happened by.

She told Thompson she was selling her unit and Thompson made arrangements to visit the condo.

Police said when he arrived Thompson robbed Calle and hit her in the head so hard he killed her.

Thompson told police he pushed Called, but she hit her head on a counter and he dragged her body into a kitchen pantry.

Authorities said Thompson, also known as Shamal Thompson, was arrested and charged Thursday morning when he was tracked down in southwest Atlanta after using one of Calle's credit cards to buy a $400 watch, clothes and shoes.

He also stole Calle's engagement ring from her hand, according to investigators.

Police said Thompson also stole her key card to the condo building and used it to get back into the building, but was turned away by security guards.

Investigators believe Thompson planned to steal more items from Calle's condo.

The victim's fiancé told investigators he found the body of Calle in her penthouse apartment.

"There did appear to be some signs of a struggle," Lt. Keith Meadows told WSB-TV Channel 2 reporter Ryan Young.

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Meadows said he believed the victim died from "blunt force trauma" to the head. She may have been dead up to 12 hours before her body was found at 11 p.m. Tuesday.

Calle was a physician and a cancer researcher, who has been the director of Analytic Epidemiology for the American Cancer Society since 1994. She was also an adjunct professor in Epidemiology at Emory University.

Calle made great contributions in the medical field, including ground-breaking research that linked cancer with obesity, according to co-workers.

Calle was engaged to be married and she and her fiancé were selling her high-rise luxury apartment.