BUFFALO, N.Y. -- Jurors on Tuesday heard a perspective from behind the bar as another employee of Molly's Pub took the stand in the Jeffrey Basil trial.

Basil is charged with murder in the death of William Sager Jr., who was launched down a flight of stairs at the Buffalo bar in May 2014. Sager died after spending weeks in a coma.

Bartender Jackson Zimmerman knew Basil from serving with him from the Air National Guard, and told the jury about an interaction between Sager and Basil before the incident.

As the jury was shown video from that night, Zimmerman explained that Rob Eloff, an off-duty Buffalo police officer who was working security that night, bought Sager a shot, courtesy of Basil, who is referred to as both the owner and manager of the bar. Zimmerman claims Sager tried to shake Basil's hand, but Basil was talking to some girls.

"He (Basil) takes Jackson the bartender aside, and he says, 'this guy's a buddy of yours, get him out of my f'in face,'" said prosecuting attorney Christopher Belling.

Zimmerman testified he didn't see Sager doing anything aggressive towards Basil. However, Adam O'Shei, another off-duty police officer working security that night, claims Basil was on a 24-hour bender, which included alcohol and pills.

"Was Mr. Basil drinking that night? Oh, you bet he was. He was throwing down double shots of Crown Royal," said defense attorney Joel Daniels.

During his cross examination, the defense established that O'Shei was given immunity in the case.

He testified that before Sager was injured, he was stumbling near a railing and Basil asked O'Shei if Sager was okay. After Basil was hurt, the defense argues O'Shei and Eloff didn't care for Sager as they should have.

"Each one had 40 hours of basic first responder training, they're experienced guys. What'd they do? They didn't even look at Mr. Sager. They didn't even examine him, they didn't check him out," Daniels said.

But O'Shei testified Sager's safety was his No. 1 priority, and that's why they carried him outside and out of potential danger. Once they did, he said he immediately told Eloff and a security guy to call 911, although the defense said it took Eloff 21 minutes.

In other testimony, a UB physics professor who provided analysis for the case said results were quite conclusive that Sager was propelled down the stairs with 374 pounds of force.

"The bang of his head hitting the floor at 17 miles an hour caused fatal damage when he hit," Belling said.

Testimony is scheduled to resume Wednesday.