Homicide detectives investigating the execution-style murder of a police informer and his wife were forced "cease all contact" with their only remaining key witness Nicola Gobbo.
Now infamous as Lawyer X, Ms Gobbo was a crucial witness in the murder case against ex-detective Paul Dale and hitman Rodney Collins for the 2004 killings of Terence and Christine Hodson.
But in a scathing statement to an inquiry into police use of informers, homicide detective Sol Solomon labelled the decision to drop her evidence as "unethical" and possibly "unlawful".
Ms Gobbo sued police in 2010 a year after agreeing to give up informing and become a witness.
Mr Solomon believes the order to end contact with Ms Gobbo was the result of a condition in the confidential settlement that she never be subpoenaed as a witness.
When he and his colleagues refused to comply they were forced to sign a document acknowledging they understood instruction to cease all contact immediately.
"I do not know who authored this document but know it came from above," Mr Solomon said.
Simon Overland was chief commissioner at the time.
The taskforce investigating the Hodson murders was also abruptly shut down and Mr Solomon said he was "banned" from calling Ms Gobbo as a witness when Mr Dale was accused of lying in Australian Crime Commission hearings.
"Deputy Commissioner (Sir Ken) Jones then advised prosecutors of a complicating fact, which was (Ms Gobbo's) writ settlement with Victoria Police included an agreement that she never be subpoenaed as a witness in the future by Victoria Police for any Victoria Police matter," Mr Solomon said.
The murder case against Mr Dale and Collins took a beating in early 2010 after the other key witness, underworld killer Carl Williams, was murdered in prison. Charges were dropped.
Williams had claimed he was a go-between for Mr Dale and Collins to arrange the murders, allegedly motivated by Mr Hodson turning informer against Mr Dale over a 2003 burglary at a drug stash house.
Mr Solomon said he'd been hopeful the prosecution could be resurrected but the order meant they couldn't contact Ms Gobbo, compel her to give evidence or even investigate her as a possible conduit for leaked material that identified Mr Hodson as a police informer.
The Petra taskforce had discovered Ms Gobbo was with Mr Dale the day Mr Hodson's informer file went missing before the murders.
"Less than 48 hours later 31 pages of information reports from the Hodson informer management file were on their way to Queensland via Tony Mokbel's fax machine," Mr Solomon said.
Mr Solomon maintains Mr Dale and Collins are responsible for the murders.
Mr Dale, who was acquitted over the ACC charges, continues to deny all allegations.
Despite being handed to Victoria Police in January, Mr Solomon's statement was only passed to the commission in May and released publicly on Tuesday night.