The first staff member the masked man saw was 67-year-old receptionist Peggy Turuhira Noble.
Without hesitation, the gunman aimed a sawn-off pump-action shotgun at her from close range.
He pulled the trigger. At least 158 shots entered her chest cavity.
Day one of Tully's murder trial in Christchurch heard from the Crown that he'd had extensive contact with Winz over the past few months.
Crown prosecutor Andrew McRae told the jury Tully was dissatisfied with his treatment and entered the building with the intent of "shooting at any staff he could see" and "killing them all".
A compilation of CCTV footage of what happened in just 61 seconds from inside the Winz building that day was shown to the jury.
After shooting Ms Noble, the Crown says Tully went further inside the building looking for more Winz workers to kill.
It's alleged he then saw Winz staff member Kim Elizabeth Adams running for an exit.
He allegedly fired at at her.
Ms Adams would later tell police she felt a "whoosh" pass her head. She ran outside to safety.
Tully then found a "terrified" Winz worker Lindy Louise Curtis hiding under a desk with a client.
The Crown allege that as Tully fired a shot at her, she moved her left leg upward, preventing a life-threatening injury.
It's alleged Tully then quickly moved to the back of the building where he found Leigh Cleveland, 55, who had the most to do with Tully in that office.
The court heard that he fired a shot at her, but as he turned to leave, allegedly went back to shoot her twice more to "ensure she was dead".
Tully then allegedly fled the scene.
The Crown say he was found beneath a macrocarpa hedge in a farmer's field near Lake Hood, across from the Ashburton River, by armed police around seven hours later after a massive manhunt.
It is alleged a piece of paper was found in his backpack which had the words, "Kim Adams", "Leigh Cleveland", and "Discrimination" written on it, which the Crown says "showed his intentions".
Tully denies charges of murdering Ms Noble and Ms Cleveland, along with attempting to murder Ms Curtis and Ms Adams.
He also denies two counts of unlawful possession of firearms, and one of setting a man trap.Tully was not present in court today - a situation explained to the jury by Justice Cameron Mander as being "an unusual situation, although not unheard of".
He is not represented in court by his own defence counsel. Instead, Tully is legally assisted by two amicus, or friends of the court, lawyers Phil Shamy and James Rapley.
About 82 witnesses are expected to give evidence in the trial, which is set down for three weeks.
It continues tomorrow at 10am.