Ross broke down on the witness stand on Thursday as he said officers grabbed Gray by the wrists and ankles and "threw him into the paddy wagon ... It was like they hog tied him."
The trial of a Baltimore police officer charged with manslaughter in the death of a young black man is due to resume on Friday, a day after prosecutors showed a video of his arrest that reduced his family to tears.
Officer William Porter has also been charged with second-degree assault and misconduct in the April death of 25-year-old Freddie Gray.
On Thursday, Gray's mother and other relatives wept as a cellphone video, taken by bystander Kevin Moore, showed Gray screaming as he was arrested and people yelling at police.
Gray died a week after being taken into custody for fleeing from an officer and possessing a knife.
Porter, 26, is one of three black officers charged in the case. He could be sentenced to more than 25 years in prison if convicted on all counts.
He is the first of six officers to go on trial in Baltimore City Circuit Court in connection with Gray's death, which triggered riots and intensified a U.S. debate on the use of excessive force by police, especially against black men.
Gray was handcuffed and shackled but not secured by a seat belt inside a police transport van. He died of an injury that prosecutors have likened to what would be suffered by a diver going into a shallow pool.
Gray's friend Brandon Ross also shot a video of a van stop in which Gray was placed in leg shackles. Ross broke down on the witness stand on Thursday as he said officers grabbed Gray by the wrists and ankles and "threw him into the paddy wagon ... It was like they hog tied him."
He identified Porter as one of the officers at the scene.
Prosecutors contend that Porter ignored Gray's request for medical assistance and failed to secure him in the van.
Defense lawyers argue that Porter had no responsibility to strap in Gray and that Gray showed no signs of illness or injury.
The other five officers face charges ranging from misconduct to second-degree murder