BROOKLYN - A witness took the stand Tuesday in the trial of an NYPD officer who shot and killed a Brooklyn man.

Melissa Butler, a friend of Akai Gurley, was visibly shaken in court Tuesday after giving her testimony in a packed courtroom. She was near Gurley when she says he was shot by NYPD Officer Peter Liang in the stairwell of the Pink Houses in 2014.

Investigators say Butler gave Gurley chest compressions before help arrived. Prosecutors asked Butler if either Officer Liang or his partner did anything to help, to which she replied no.

The prosecution is building a case that Liang had the correct CPR and firearm training provided by the NYPD as a recruit.

Also in court, jurors got the chance to see and hold the handgun that fired the deadly shot at Gurley. The jurors were allowed to touch and hold the gun, and even pull the trigger with help from the court officer.

Liang is expected to take the witness stand later in the proceedings. If convicted, he faces up to 15 years in prison.