Victoria's top cop on when the scourge of firebombings will stop

Victoria's police commissioner says investigating organised crime in the construction industry will be a "long journey", as detectives work to build evidence and reassure intimidated witnesses.

Chief Commissioner Mike Bush says police have made dozens of arrests over Melbourne's many firebombings, but are focused on identifying those directing the attacks.

He says police are reviewing how police stations are staffed, with priority given to getting police officers out on the street.

Victoria's police chief says investigators are working to reassure witnesses facing "violence and intimidation" from criminals in the construction sector, with police still yet to lay any charges related to corruption on taxpayer-funded Big Build sites.

In an interview with 774 ABC Melbourne, Chief Commissioner Mike Bush said it would be "long journey" for police investigating organised crime in the construction industry to build the necessary evidence base to bring charges relating to corruption and crime in the sector.

Taskforce Hawk was established two years ago to target crime in the construction sector and major Victorian government infrastructure projects, including the infiltration of outlaw motorcycle gangs.

Chief Commissioner Bush and the ABC's Raf Epstein during their wide-ranging interview. (ABC News: Darryl Torpy)

"Our team have been working really well to reassure them, to keep them safe, and bring those people forward, so those arrests are based upon people who are finally feeling reassured that we are here for them, that we'll look after them.

"But that's quite a long journey. Again, if you think about the modus operandi of the people who are committing these crimes it's pure violence and intimidation."

On Wednesday detectives from Taskforce Hawk arrested underworld figure Mick Gatto before releasing him without charge.

Mr Gatto, a self-described "mediator and arbitrator" in the construction industry, was named in a report for Queensland's Commission of Inquiry into the CFMEU last year as a "malignant influence" who maintains criminal associations.

Mick Gatto was arrested on Wednesday and released without charge. (AAP: Morgan Hancock)

He also declined to say if any criminal charges could be expected from Taskforce Hawk's investigations.

"We are going to work very hard towards holding anyone to account that is involved in corruption, whether it be Big Build [sites], or any construction where corruption is concerned," Commissioner Bush said.

"Before we can charge people, before we can put matters before the court, we absolutely need the evidence. Par