West Midlands Police's chief constable has been ordered to produce any information surrounding a claim the force may have been tipped off in advance of the Birmingham pub bombings by an IRA "mole".
A coroner made the order on Wednesday after hearing legal submissions on whether there was enough evidence to resume an inquest into the 21 deaths in 1974.
Louise Hunt, the senior coroner for Birmingham and Solihull, said she was adjourning proceedings because of an "evidential vacuum" around claims made by the victims' families' lawyers.
Earlier, Ashley Underwood QC representing three of families, had said: "There is reason to believe the gang of murderers had an informant in their ranks and that the police knew in advance.
"And there is reason to believe the police had sufficient time, between the telephone warnings and the first bomb going off, to evacuate - and that the emergency services could have arrived earlier - but that records about those things were falsified."
He added: "But if it is (true), then the police had a mole in the gang which raises the question, did they know it was going to happen and did they lie to the (criminal) court to cover their knowledge of that, and cover their mole."
The force's barrister Jeremy Johnson QC told Ms Hunt that chief constable Dave Thompson had "no principled objection to the resumption" but questioned whether the coroner had any legal jurisdiction to do so.
However, he added West Midlands Police would comply with the coroner's direction to supply any documents, statements and supporting evidence on a number of key factors raised by the families.
He also said the criminal investigation was still open.
On the night of November 21 1974, devastating blasts ripped through the city centre Tavern in the Town and the Mulberry Bush pubs, packed with pre-Christmas revellers.
The fatal bombings, which also left 182 people injured, are widely acknowledged to have been carried out by the IRA.
A subsequent police investigation led to the wrongful convictions of the Birmingham Six, who were released in 1991 after their convictions for murder were overturned by the Court of Appeal.
One of their number, Paddy Hill, was at the coroners court on Wednesday to hear proceedings.
Concluding the first of what was scheduled to be three days of submissions, Ms Hunt said she needed more information before making any decision on a resumption of the original inquests.
Making her order, the coroner asked for any information held by the police "in relation to the timing of the bombings and any evidence that the State had advance notice of the bombings".
She also asked the force for any evidence held surrounding "whether or not there was an informant", and whether the response to telephoned bomb warnings was delayed.
The police must also now disclose anything relating to "falsification of documents by West Midlands Police for the purposes of protecting any informants or anyone else".
A summary of the previous police investigations carried out since 1991 was also requested, along with a list of "lost" and destroyed evidence from the original criminal investigation.
An internal police review ending in 2014 found that of 168 original exhibits listed for the Birmingham Six trial, 35 items could not be located.
All the information must be provided to the coroner by March 4, added Ms Hunt, along with a statement from a senior officer which can be made public.
Addressing the families at the hearing in Solihull, West Midlands, she said: "I know you've waited a long time and it's never helpful to wait a little longer but I want to get everything right."
Earlier, she described the events of that night as "a terrible atrocity resulting in the deaths of innocent people and serious injury to many more".
Outlining the current state of the police's criminal investigation into the bombings, Mr Johnson said there had been three developments in the case including new potential forensic evidence, a book by former IRA spymaster Kieran Conway, and a first-hand account from now dead West Midlands fireman Alan Hill.
Inquests were opened and adjourned at the time, but never resumed as a result of the Birmingham Six's convictions in August 1975.
Speaking outside court after the hearing, Julie Hambleton - whose then 18-year-old sister Maxine was killed by the Tavern bomb - said the families had been "left in limbo by West Midlands Police".
A provisional decision date has been set by the coroner for April 6.