The 29-year-old journalist was shot dead on Thursday night in Creggan by a masked gunman who fired at an armoured police vehicle and hit Lyra in the head with a bullet.
The writer and author was standing beside the police vehicle when she was hit.
Two men – aged 18 and 19 – who were arrested on Saturday morning under the Terrorism Act – were released unconditionally on Easter Sunday evening by detectives.
Detective Superintendent Jason Murphy of MIT said: “We have received very positive support from the community but we need to convert this support into tangible evidence that will enable us to bring Lyra’s killers to justice.
“We will continue to work positively and sensitively with the local community to achieve this.
“I am continuing to appeal for those people who were in Fanad Drive and Central Drive on Thursday night and who have mobile phone footage to please come and speak with my detectives and provide us with your mobile phone footage.
“We do not need to hold on to your phone, we have necessary equipment that will allow us to download the footage quickly.
“Alternatively, you can use the Major Incident Public Portal at www.MIPP.police.uk
“I know there will be some people who know what happened but are scared to come forward.
“But if you have information, no matter how small, please contact detectives in the incident room on 101 or via the Crimestoppers charity on freephone 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”
A funeral service will be held for Lyra on Wednesday at 1 pm in St Anne’s Cathedral in Belfast.