ORLANDO, Fla. (AP) — A body found in Tampa Bay has been identified as the second missing University of South Florida doctoral student from Bangladesh, a sheriff said Friday. He described their killings as “a monstrous crime.”

Nahida Bristy’s remains were found Sunday in a garbage bag discovered by a kayaker whose fishing line got snagged, said Hillsborough County Sheriff Chad Chronister.

The positive identification on the badly decomposed body was eventually made using DNA and dental records, he said.

The body of her friend, fellow USF doctoral student Zamil Limon, was in another garbage bag found two days before that on a bridge over the bay.

Limon’s roommate, Hisham Saleh Abugharbieh, 26, was taken into custody the same day and has been jailed since then, facing two charges of first-degree murder.

Chronister said the suspect showed no emotion when investigators presented him with details of the killings.

“He was nonreactive,” Chronister said. “He was callous and showed no emotion when we showed him the information we had.”

The two students were murdered around the same time and place, though more investigation is needed before detectives can decide that conclusively, the sheriff said.

A motive for the killings remains unknown, he said. “I hope we find that out.”

The students’ disappearances on April 16 started off as separate missing persons’ cases for the campus police and the sheriff’s office, involving two responsible individuals for whom missing appointments was very uncharacteristic. But investigators soon realized they were connected, the sheriff said.

Detectives first went to the apartment Limon shared with Abugharbieh and a third roommate. The other roommate was cooperative while Abugharbieh gave elusive and inconsistent answers, the sheriff said.

He also had a bandaged finger and a cut on his arm that should have been stitched up. It was enough to make him a ‘person of interest,’ but not to merit an arrest.

They went to interview the roommate again, alone this time, and he told them Abugharbieh had used a large cart to move things out of his room to a trash compactor overnight on April 16 and 17.

The first break in the case came when investigators searched the trash compactor and found Limon’s glasses, his student ID card, his wallet and his blood-covered clothes.

The discovery gave law enforcement enough evidence to get a search warrant for the apartment itself and the suspect’s electronic devices, Chronister said.

A search of the apartment showed large traces of blood in the kitchen, leading down the hall and to inside Abugharbieh’s room.

A blood-detecting spray even revealed blood in the shape of a human body curled up in the fetal position, next to Abugharbieh’s bed, the sheriff said.

Traces of blood were also found on the floorboards of Abugharbieh’s car, Chronister said. Tests would later reveal it was Bristy’s.

Investigators believe the bodies were moved to the car in a cart, under the cover of darkness, he said.

Using the GPS of the suspect’s car and surveillance video from a fire station, investigators determined that Abugharbieh drove over to Clearwater and across the Tampa Bay bridge, leading investigators to start an extensive search along his route.

Chronister said content on Abugharbieh’s phone had been erased, but a forensic examination revealed disturbing searches in the days before Bristy and Limon went missing.

The searches included phrases like, “Can a knife penetrate a skull?” and “Can a neighbor hear a gunshot?”

The suspect had also purchased Lysol wipes, heavy-duty contractor-grade trash bags and other equipment before April 16, he said.

“This was calculating. That’s what makes this so premeditated,” Chronister said.

The sheriff said the victims’ relatives have been notified.

Limon was studying geography, environmental science and policy, and Bristy was studying chemical engineering. Abugharbieh had dropped out of the university.

Reached by email earlier this week, Jennifer Spradley, an attorney in the public defender’s office in Tampa, said the office wouldn’t comment on Abugharbieh’s case.