Joseph Caballer, a former Marine sergeant, said he had given Penny martial arts instruction and explained a "blood choke" designed ... the person performing the hold wasn't applying pressure.

When Daniel Penny wrapped his arm around the neck of a homeless man on a Manhattan subway last year, the 25-year-old veteran appeared to be deploying a non-lethal chokehold long drilled into U.S.

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