POLICE have named the gunman who killed a 43-year-old solicitor and critically injured two others in a cold-blooded CBD shooting today.
Christopher Wayne Hudson, 29, who has an involvement with the Hell's Angels, is being sought by police in connection with the shooting.
The killer callously opened fire on an innocent jogger and pedestrian who came to the aid of a woman he was dragging by the hair from a taxi.
Det-Insp Stephen Clark of the homicide squad said the dead solicitor's last act ``was one of extreme bravery''.
``It's a tragic, tragic set of circumstances and it does appear as though he's been in the wrong place at the wrong time and has gone to the assistance of a female. It really strikes at the heart of all investigators to see somebody who's going about their daily life to be killed in such a tragic way,'' he said.
The gunman ran off after shooting the three people on the corner of Flinders Lane and William St at 8.15am. Earlier, he punched an exotic dancer in the face at the nearby Barcode 24-hour venue in King St.
This afternoon police revealed they know who the gunman is and have issued warrants for his arrest across Australia. They also revealed the the good Samaritan who was killed trying to help the girl is a 43-year-old lawyer.
The other man who attempted to help is 30 and reported to be in a critical condition in hospital.
Det-Insp Clark said the investigation was currently the force's number one priority, and called on the gunman to hand himself in.
Eyewitness Zali said the gunman was "as cool as a cucumber" as he cold-bloodedly blasted his victims.
"He just went bang, bang, bang, there was no mucking around," she told ABC Radio.
"There were five shots fired and the people went straight down to the ground. There wasn't even a scream, just a whimper."
Witnesses reported hearing six or seven shots in the area before police and emergency services arrived.
One man was shot in the chest and died in the street after paramedics worked frantically on him for almost an hour.
The woman, 24, is thought to know the shooter. She and the other man, 30, had emergency surgery in the Royal Melbourne Hospital.
The exotic dancer, believed to work at the Spearmint Rhino, is also being treated in hospital for minor injuries.
Police recovered a semi-automatic handgun and discarded black jacket at a nearby building site about two hours after the shooting.
It is understood the gunman may have thrown the weapon as he fled the scene.
Hundreds of office workers were ordered to remain inside in the shooting aftermath. Some barricaded furniture against doors.
Police describe the gunman as about 180cm, aged late 20s to early 30s, with short brown hair and wearing a dark Adidas tracksuit top and dark denim jeans.
Dozens of building workers where a worker found the gun were told to leave the site as police cordoned off the area. And schools have been ordered to cancel any excursions into the city today.
Detectives are checking security camera footage from the club where the gunman was involved in a fight.
Melbourne's city centre was in shutdown as police searched the area for the shooter, with offices sealed off and people kept away from nearby workplaces.
Carly, who was in the Rialto building on Collins Street, said people in her building had been told not to move.
"We've just been told that none of our people who are waiting downstairs to come upstairs can come up," Carly told 3AW.
"They've blocked off all the access to the floors in our building because they're still looking for the shooter.
"We're not allowed to go anywhere and no one is allowed to come up into the building."
Carly said she had heard six or seven shots.
Malcolm Bates said that before the shooting broke out the gunman grabbed a woman by the neck as she sat in a taxi, and tried to get into the vehicle.
"The lady got away and he turned and shot three people basically point blank," Mr Bates said. "I was right across the road."
He told ABC radio the gunman then ran down Flinders Lane toward the city centre.
He said the entire incident took no longer than "the wink of an eye".
Police wearing bullet-proof vests were scouring the area and police helicopters hovered overhead.
Insp Glenn Weir said the last confirmed sighting of the gunman was east of the shooting scene, on Flinders Lane.
One witness rang her mother and said: "Mum, I've just witnessed this horrible shooting, I have to go." She reported seeing people lying in the street.
Another witness, Peter, said he rang emergency services after coming across the scene, but he initially thought it was a car crash with three people in the gutter and on the street.
"The people who were standing around didn't seem to be perturbed by anyone with a gun, it was almost as if there had been a car accident," Peter said.
The crime scene triggered peak-hour traffic chaos.
The intersection of Flinders Lane and William St was closed.
Flinders and Queensbridge streets have been re-opened but William St will remain closed for some time.
Police in Melbourne, Australia are on the hunt for a gunman who killed a man and injured two others in the city's central business district this morning. 

Officials warned all office workers to remain indoors, and train services to Flinders Street Station were temporarily on hold, as investigations were carried out on the intersection of Flinders Lane and William Street.

Malcom Bates, who witnessed the shootings at around 8:15 a.m., said the gunman grabbed a woman from inside a taxi. "The lady got away and he turned and shot three people basically point blank," Mr Bates said. "I was right across the road". He said that the incident took no longer than the "wink of an eye".

Paramedics struggled to revive the one victim for almost an hour before declaring him dead at the scene. The two injured people have been taken to the Royal Melbourne Hospital in a critical condition.

Police believe the incident began at the Bar Code 24-hour bar in King Street, when a woman attempted to get into a taxi. She was apparently grabbed by the hair by the gunman who then shot her and two men who attempted to come to her aid.

Police have identified the gunman as Christopher Wayne Hudson, aged 29. They believe him to be a member of the Hells Angels bikie gang. Police have described Hudson as about 180 cm tall, with short brown hair and wearing a dark tracksuit top and dark denim jeans.

A building worker on a construction site on the corner of Queen and Flinders Streets has reportedly discovered a handgun. It is understood the gunman may have thrown the weapon into the site as he fled the scene.