In December last year Monis walked into the Lindt cafe in Martin Place armed with a gun and Islamist flags, triggering a siege that led to the deaths of two hostages. Foreign Affairs Minister Julie Bishop pictured on June 4 tabling a letter after adding to an answer on Man Haron Monis writing to Attorney-General Senator George Brandis. Credit:Andrew Meares But a joint Commonwealth-NSW inquiry into the siege never examined his letter to Senator Brandis because an official didn't realise it was on the second tab of a spreadsheet. Foreign Affairs Minister Julie Bishop told Parliament - based on mistaken evidence from an official - that the letter had been sent to the inquiry. She eventually corrected the record but did not do it until the end of a sitting fortnight, meaning the government avoided scrutiny in question time about its handling of the case. Ms Bishop was overseas a the start of the week and did not return to Parliament until the Thursday.

A Senate committee has already discovered Senator Brandis and Mr Abbott's office knew about the letter at the start of the sitting week. Ms Bishop was overseas a the start of that week and did not return to Parliament until the Thursday. Lindt cafe gunman Man Haron Monis, pictured in 2010 - four years before the siege, was praised by the Islamic State publication Rumiyah. Credit:Kate Geraghty However, the new emails show a 'PPQ' - a briefing about possible lines of attack on the issue from Labor in question time - was prepared for Mr Abbott on Monday, June 1 - three days before Ms Bishop made the correction on June 4. The brief - prepared by the second-in-charge at the Department of Prime Minister and Cabinet - explicitly stated the inquiry was never given the Monis letter. The brief was emailed to an unnamed official at 11.50am. Question time commended at 2pm.

However Labor did not ask any questions about the issue that day, so Mr Abbott did not need to use the brief. It is unclear whether he read it. It's time for the Prime Minster to tell the truth about what happened here A spokesman for Mr Abbott did not answer questions about whether the Prime Minister had read the question time briefing. Labor's leader of the opposition in the Senate, Senator Penny Wong, accused the government of a cover-up. "It's time for the Prime Minster to tell the truth about what happened here," she said.

"The Prime Minister cannot continue to duck questions about the part he and his office played in this cover-up. The Prime Minister is accountable for this cover-up." Senator Wong also said ministers have resigned over misleading the Parliament in the past. A spokesman for Mr Abbott said a "thorough review" was undertaken by the Attorney-General's Department once it became clear in July that the letter had not been sent. "As soon as that review was completed, the record was corrected by the Attorney-General and by the Foreign Minister." The spokesman also said Department of Prime Minister and Cabinet secretary Michael Thawley - one of the two bureaucrats who conducted the inquiry - has noted the letter would have made no difference to its findings even if it had been seen.

TIMELINE October 7, 2014: Man Monis writes to Attorney-General George Brandis December 16, 2014: Sydney siege ends with the killing of two hostages and the death of Monis December 17, 2015: Tony Abbott announces a joint Commonwealth-NSW inquiry January 31, 2015: Inquiry is delivered to Mr Abbott

February 2, 2015: Attorney-General's Department realises Monis letter never went to inquiry February 2, 2015: Department contacts review team by phone but told the document did not need to be provided because the review had been concluded February 4: Inquiry authors sign off report for printing May 27, 2015: Department official tells Senate estimates hearing the letter had been sent May 28, 2015: Julie Bishop quotes that official's evidence to deflect Labor attack about why the Monis letter didn't raise red flags

June 1, 2015: Prime Minister's Office and Attorney-General told the letter did not go to the inquiry. Question time briefing prepared for Tony Abbott explicitly states the inquiry was never given the Monis letter Loading June 4, 2015: Julie Bishop corrects the record at the end of the last question time for that sitting fortnight Follow us on Twitter