Inspector Richard Dee testified Tuesday at Officer Daniel Pantaleo's internal trial, nearly five years after Garner's pleas of "I can't breathe" became a rallying cry against police brutality.
Dee also says that coughing heard on the video indicates Garner's breathing was restricted by the hold.
Dee says recruits are explicitly warned that chokeholds are banned, and they are instructed to disengage when they realize they're using a chokehold.
Pantaleo is accused of hastening Garner's death. His lawyer says the officer used an approved technique known as a "seat-belt hold," but Dee says there is no record of Pantaleo's receiving training in that move.
On Monday, protesters blocked traffic on the FDR Drive as the disciplinary trial got underway.
The protest included members of the activist group Black Lives Matter Greater New York. There were no reports of arrests.
Pantaleo could face penalties ranging from the loss of vacation days to firing if he's found to have violated department rules.
He is not required to be in court as it is a departmental trial, and he denies wrongdoing.
A ruling last week requires that the police watchdog agency bringing the case prove not only that Pantaleo violated department rules, but that his actions fit the criteria for criminal charges.
Pantaleo does not actually face criminal charges, but he has been on desk duty since Garner's death.
Garner's mother Gwen Carr says it has been a long five years.
"They've tried every trick in the book to keep the case from going forward. We've all seen Eric being murdered on video," she said. "It wasn't just me, it wasn't just an eyewitness. It was all of us who've seen Eric being murdered on camera."
(The Associated Press contributed to this report)
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