By Melanie Burton and Tom Westbrook
MELBOURNE (Reuters) - Australian counter-terrorism investigators were searching two properties in suburban Melbourne on Saturday morning, the day after a man killed one person in what authorities said was a terrorist attack in the city.
Police identified the attacker as 30-year-old Hassan Khalif Shire Ali, and said that his brother was arrested last year on charges of planning an attack in Melbourne. They had earlier said he was 31 years old.
Shire Ali had set fire to a pickup truck laden with gas cylinders in the centre of Melbourne on Friday and stabbed three people, killing one, before he was shot by police.
"Joint Counter Terrorism Team investigators are executing search warrants at two addresses in Werribee and Meadows Heights this morning" Victoria police said in a statement. "More information will be provided when it's appropriate to do so."
Earlier, Victoria Police Commissioner Graham Ashton said in a television interview that Shire Ali was known to authorities because of his brother, and also had driving, theft and cannabis offences.
"He is certainly someone who is known to both us and the federal authorities in relation to counter-terrorism and terrorism-related matters," he told Channel 7's Sunrise programme.
"He is the brother of an offender or a suspect that we arrested late last year in relation to the preparation of a terrorist event."
His brother was arrested in a dramatic raid last November. Police said then they believed he was an Islamic State sympathiser and was planning an attack Melbourne's central Federation Square on New Year's Eve in 2017. He is in jail awaiting trial.
Islamic State claimed responsibility for Friday's attack, but that could not be substantiated and police have not commented on it yet.
The attack began just before the evening rush hour and lasted only minutes. While the utility truck carrying barbecue gas cylinders burned on busy Bourke Street, Shire Ali stabbed bystanders and attacked police. (https://tmsnrt.rs/2Qu5stX https://tmsnrt.rs/2Qu5stX))
The cylinders did not explode and the fire was put out in 10 minutes, by which point the attack was over, though not before one man was fatally stabbed.
Video posted to Twitter and broadcast on television showed the man swinging a knife at two police officers, before he collapsed when one shot him in the chest. He later died in hospital.
Bourke Street reopened on Saturday morning, and a Reuters reporter said there was an increased police presence in the area.
A staunch U.S. ally, Australia has been on alert for such violence after a Sydney cafe siege in 2014, and its intelligence agencies have stepped up scrutiny, though Ashton said there was no warning of the latest attack.
He said there was no longer a threat to the public, but that security would be boosted at horse races and Remembrance Day memorials over the weekend. Sunday marks 100 years since the armistice was signed that marked the end of World War One.
Authorities say Australia's vigilance has helped foil at least a dozen plots, including a plan to attack Melbourne at Christmas in 2016, Shire Ali's brother's scheme and a plan to blow up a flight from Sydney using a bomb disguised as a mincer.
In December 2014, two hostages were killed during a 17-hour siege by a "lone wolf" gunman, inspired by Islamic State militants, in a cafe in Sydney.
(Reporting by Tom Westbrook in SYDNEY and Melanie Burton in Melbourne; editing by Richard Balmforth and Diane Craft)