(CNN) In the last moments before his death, 49-year-old anesthesiologist Richard Field texted a friend pleading for help.

"I was confused for the first minutes," Matthias Heidenreich testified last week in the first days of the double murder trial for the man suspected of killing Field and his 38-year-old fiancée, Lina Bolanos.

"I did not realize what (the text) means, wasn't sure what it is," Heidenreich said.

The couple, both well-known anesthesiologists, were stabbed to death in their Boston penthouse in May 2017.

In the texts, Field tried to ask Heidenreich to call 911 because an armed man was in his home.

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