The killer who blew up one of the journalists behind the Panama Papers investigation detonated the bomb remotely with a mobile phone, detectives believe.
Renowned blogger Daphne Caruana Galizia, 53, was killed in the explosion as she left her home in northern Malta.
The killing shocked the small Mediterranean island and Prime Minister, Joseph Muscat, promised a cash reward to anyone who came forward with information about the murder.
But her three sons have dismissed the reward and instead demanded that Muscat resign.
Muscat flew to Brussels on Thursday for an EU summit, where his spokeswoman said investigators were making progress with their investigation.
She said: “Emerging evidences make us think that the bomb was placed under the car and was set off with a remote trigger.”
Foreign experts will help identify the mobile phone which was used to detonate the bomb, she added.
Police commissioner Lawrence Cutajar denied British detectives would join Dutch forensic experts and the FBI in helping with the investigation, reports the Huffington Post .
His statement contradicted Muscat’s spokeswoman, who earlier said that British officers would be involved.
Ms Galizia's son Matthew Caruana Galizia, a journalist himself, was at home when his mother Daphne Caruana Galizia, 53, was killed .
She had filed a complaint to police a fortnight before her death after receiving personal threats to her safety, local media said.
Caruana Galizia ran a hugely popular blog relentlessly highlighting cases of alleged corruption, often involving politicians from the Mediterranean island nation.
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Earlier this week Mr Galizia lashed out at the authorities for failing to protect his mother.
In a Facebook post he wrote: "My mother was assassinated because she stood between the rule of law and those who sought to violate it, like many strong journalists.
"But she was also targeted because she was the only person doing so.
"This is what happens when the institutions of the state are incapacitated: the last person left standing is often a journalist.
"Which makes her the first person left dead.
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"I am never going to forget, running around the inferno in the field, trying to figure out a way to open the door, the horn of the car still blaring, screaming at two policemen who turned up with a single fire extinguisher to use it.
"They stared at me. “I’m sorry, there is nothing we can do”, one of them said.
"I looked down and there were my mother’s body parts all around me. I realised they were right, it was hopeless.
“Who is in the car?”, they asked me. “My mother is in the car. She is dead. She is dead because of your incompetence.”
Maltese Prime Minister Joseph Muscat, who faced accusations of wrong-doing by Caruana Galizia earlier this year, denounced her killing.
He called it a "barbaric attack on press freedom".
Mr Galizia continued on Facebook: "A few hours later, while that clown of a Prime Minister was making statements to parliament about a journalist he spent over a decade demonising and harassing, one of the police sergeants who is supposed to be investigating her murder, Ramon Mifsud, posted on Facebook, 'Everyone gets what they deserve, cow dung! Feeling happy :)'"
He continued: "Yes, this is where we are: a mafia state where you can now change your gender on your ID card (thank God for that!) but where you will be blown to pieces for exercising your basic freedoms. How did we get here?
"A culture of impunity has been allowed to flourish by the government in Malta.
"It is of little comfort for the Prime Minister of this country to say that he will “not rest” until the perpetrators are found, when he heads a government that encouraged that same impunity.
"If the institutions were already working, there would be no assassination to investigate - and my brothers and I would still have a mother."
Muscat had called early elections in June seeking a vote of confidence to counter Caruana Galizia's allegations of corruption.
The report had said documents in a small Malta-based bank showed that Muscat's wife was the beneficial owner of a company in Panama, and that large sums of money had been moved between the company and bank accounts in Azerbaijan.
Both Muscat and his wife denied the accusation and sued Caruana Galizia for defamation.