The military trainer said that Marines are taught to render a person unconscious in seconds. Mr. Penny held Jordan Neely, a homeless man, for six minutes.

Joseph Caballer, a nine-year veteran of the corps who trained troops in self-defense, told the jury Daniel Penny's elbow and hand were "not in the correct position" for a proper figure-four chokehold and he could have been cutting off Jordan Neely's windpipe.

In the trial of Daniel Penny, a man accused of killing a homeless and mentally ill man on the New York City subway, jurors are hearing from experts on chokeholds following an admission from a key witness that he lied to police.