As lawyers for Daniel Penny, a former Marine accused of choking a homeless man to death in a New York subway car, vetted jurors Friday, a woman sat at a courtroom table, leaning toward the people being questioned and scribbling in a notebook.

The woman, Jo-Ellan Dimitrius, a jury consultant for the defendant, has been in Manhattan criminal court every day as scores of prospective jurors arrive for selection in a case that has divided New Yorkers from the moment the video of Mr. Penny holding the homeless man, Jordan Neely, on the subway floor ricocheted around the internet in May 2023.

However, Mr. Penny, who faces charges of manslaughter and criminally negligent homicide, is far from her most high-profile client.

Ms. Dimitrius, whose clients have spanned the spectrum from celebrities to corporations to the president of Brazil, worked with lawyers for Kyle Rittenhouse, who in 2021 was acquitted of killing two people and wounding another at a Black Lives Matter rally in Wisconsin. In 1994, O.J. Simpson’s team hired her to help select a favorable jury. Before that, she worked with defense lawyers in three cases that arose from the beating of Rodney G. King by Los Angeles police officers in 1991, an episode that set off rioting.

The presence of Ms. Dimitrius highlights the charged atmosphere surrounding Mr. Penny’fs trial, and the intense scrutiny trained on those who will decide it, a group that a judge ruled this week would remain anonymous to the public.

Mr. Penny has said that he restrained Mr. Neely, who had a history of mental illness, after he boarded an F train and threatened riders. While some New Yorkers saw Mr. Penny’s efforts that May 1 afternoon as acts of aggression that needed to be swiftly prosecuted, others saw them as the embodiment of transit riders’ fears and frustrations.