New York (CNN) -- Timothy Haydock, an emergency room physician and Kennedy family friend, is expected to take the stand Thursday in the trial of the son of the late Robert F. Kennedy.
Douglas Kennedy is accused of twisting one nurse's arm and kicking another in January as he tried to leave the maternity ward of a suburban New York hospital with his newborn son.
Haydock, who was with Kennedy at the time of the incident, previously asserted that the "nurses were the only aggressors" and is considered a key witness for the defense.
His testimony is expected to fit the defense's narrative that Kennedy's actions, which were in part captured on hospital surveillance video, were the result of an overly aggressive hospital staff and the product of a father's instincts to protect his child.
Judge John Donahue -- not a jury -- is hearing the case involving misdemeanor charges of harassment and child endangerment.
Kicking off the trial, the two sides outlined significantly divergent scenarios of what happened at Northern Westchester Hospital.
One of the nurses, Anna Lane, testified Monday that she'd initially reached in to hold open an elevator door to prevent Kennedy from leaving that way. When he headed toward a stairway door, she ran to it and put her hand on the doorknob.
"I had my hand behind my back and he grabbed my left hand -- which was on the doorknob -- and twisted my arm," said Lane.
Kennedy raised his foot and kicked another nurse, Cari Luciano, who'd come to help before entering the stairway, Lane added. But he only got down as far as the next landing, where he was met by security.
The defense team was tough on the nurse. Suggesting she had an ulterior motive given Kennedy's high profile, lawyer Robert Gottlieb questioned a tearful Lane why, if recounting her story was so emotionally difficult, she had recounted her version of what happened so soon after the incident on NBC's "Today Show."
After Kennedy was arraigned in February, his attorney released a statement stating that nurses initially agreed to let him take the baby outside and demanding "appropriate disciplinary action" be taken against Lane and Luciano.