The leader of the Scottish Liberal Democrats has asked the Lord Advocate to confirm the Lockerbie bombing is still being "rigorously and actively investigated".
Willie Rennie said the relatives of the victims of the Lockerbie bombing need assurances that the live investigation is still being fully resourced and supported.
Following the death of Abdelbaset al-Megrahi, who remains the only man to be convicted in connection with the bombing, Lord Advocate Frank Mulholland met the interim Libyan prime minister to discuss the investigation of others involved in the crime.
As well as murder, Al-Megrahi was convicted of conspiracy to murder during his trial at Camp Zeist in the Netherlands, a charge which stated that he acted with others to kill the 270 people who died at Lockerbie in December 1988.
Mr Rennie said investigating officers from Dumfries and Galloway Constabulary had not yet been to Libya to follow up on enquiries.
In a letter to Mr Mulholland he wrote: "In May this year you said: 'The investigation into the Lockerbie bombing will continue, to bring to justice the others involved in this act of state-sponsored terrorism.'
"I hope this is still the case and you can provide assurances that the Lockerbie bombing is still being rigorously and actively investigated."
Mr Rennie had previously backed calls in the Scottish Parliament for an inquiry into the Lockerbie prosecution.
He said: "Earlier this year the First Minister rejected calls for an independent inquiry into the Lockerbie prosecution, which could have shone a light on the extent of Megrahi's involvement or even pointed towards others being involved.
"In denying that independent inquiry the opportunity to get the answers so deserved by relatives of the Lockerbie bombing it was left to the criminal investigation.
"It's therefore hugely disappointing that Scottish police officers have yet to visit Libya to undertake their investigation.
"With the passing of each month it becomes less and less likely that any existing evidence can be found.
"The Crown's position that Megrahi did not act alone is all very well, but it brings neither justice nor answers to those who need it most."