(CNN) A chilling 911 call may have captured Lina Bolanos' last moments, who was killed alongside her fiancé in their Boston penthouse .

"That was Lina's voice," Amanda Gibbs, Bolanos' godmother, confirmed on the witness stand Monday after listening to the 911 call, CNN affiliate WBZ reported.

But in the call, Bolanos' voice came out muffled. And when she was unable to respond to repeated questions, the operator said she was "releasing the call"and hung up, CNN affiliate WCVB reported.

Jurors heard that phone call on the third day of testimony in the double murder trial for the man suspected of killing the couple. Bolanos, 38, and Richard Field, 49, who were both well-known anesthesiologists, were stabbed to death in May 2017.

Prosecutors say the couple was killed by Bampumim Teixeira, who briefly worked as a concierge at the building where the couple lived. Because of his time there, Teixeira was familiar with the building's layout, the Suffolk County District Attorney's office said in a news release in 2017.

Teixeira has pleaded not guilty.

"(Field was found) dead in a pool of his own blood. His hands bound behind his back with handcuffs," Assistant District Attorney John Pappas said in trial last week, according to WCVB. "Lina Bolanos was also in a pool of her blood after having been stabbed repeatedly in the neck."

Bampumim Teixeira

"No credible evidence will tell you that Bampumim Teixeira broke into the home of Lina Bolanos and Richard Field and murdered them," defense attorney Steven Sack said in the trial last week. "And that's because he didn't."

'You guys are going to die'

On May 5, a person wearing gloves, a bright yellow shirt, a hooded jacket and carrying a backpack sneaked into the building's garage before the couple returned home, according to the news release from the district attorney's office.

Later that evening, Matthias Heidenreich -- a friend of the two doctors -- received a series of texts from Field that a gunman was in their apartment and to call 911, according to his testimony last week. He testified he responded but got no answer.

Authorities were first contacted around 8:30 p.m. by the concierge, who had been alerted by a concerned friend following a text from Field, the release said.

Upon responding to the grisly scene, Boston police officer Scott MacIsaac testified Monday he shot Teixeira as he entered the couple's apartment after he saw a silhouette seemingly holding a firearm, WCVB reported.

Boston police detective Sean Wallace testified he saw Bampumim Teixeira, charged with killing two Boston doctors, smiling up at him as he was being arrested

When Texeira was taken into custody in the hallway, he told police there were dead bodies in the penthouse, Boston police detective Sean Wallace testified.

"Then he said, 'you guys are going to die.' Then he said, 'they killed my wife.' Then he mentioned something and I heard the word 'sniper,''' the detective said in court.

"He was smiling up at me," Wallace testified.

Outside the apartment, police found a backpack with a replica firearm and jewelry, the release said. A carving knife and a bright yellow shirt were also found nearby, the release said.