A Bronx man seen in a video last year helping Daniel Penny restrain a homeless man on a subway car floor testified on Tuesday that he stepped in thinking that his assistance would mean that Mr. Penny would release his chokehold.

The man, Eric Gonzalez, told jurors in Mr. Penny’s manslaughter trial that he had entered the subway at Broadway-Lafayette Street station on May 1, 2023, and came upon the men — Mr. Penny and Jordan Neely — struggling on the floor. Mr. Penny had his arms around Mr. Neely’s neck and his legs around his waist. Mr. Gonzalez said he immediately waved his hand before Mr. Penny to get his attention and let him know that he would hold Mr. Neely’s arms.

Mr. Gonzalez, whom prosecutors had called to the stand, said that he thought that if he helped, then Mr. Penny might adjust his hold on the other man’s neck. When Mr. Penny didn’t, Mr. Gonzalez held Mr. Neely anyway.

As the minutes ticked by, Mr. Neely began to struggle, shifting and trying to break free. Eventually, Mr. Neely went limp and the men let go, he said.

“I tried to shake Jordan Neely to get a response out of him,” Mr. Gonzalez said. He tried to put Mr. Neely in a “recovery position” on his side, felt for a pulse then “I walked away.”

Last year, footage of Mr. Penny choking Mr. Neely, a Michael Jackson impersonator with a history of mental illness, reverberated across the internet. Some New Yorkers saw Mr. Penny’s act as criminal and others saw his actions as the manifestation of transit riders’ fears and frustrations.