27/04/2016 4:07 PM AEST | Updated 03/08/2016 12:44 AM AEST

New Terror Charges Laid On Four Men Over Curtis Cheng Shooting

Pool via Getty Images
SYDNEY, AUSTRALIA - OCTOBER 17: People arrive for a funeral service for Curtis Cheng at St Mary's Cathedral October 17, 2015 in Sydney, Australia. Police employee, Curtis Cheng, was shot outside the NSW police headquarters in Parramatta two weeks ago by an Iranian born Australian. Australian Prime Minister Malcolm Turnbull has called the murder an 'act of terrorism.' (Photo by Tim Hunter.-Pool/Getty Images)

A fourth man has been charged over the fatal shooting of police accountant Curtis Cheng, with new terror charges laid against three other men.

Cheng was shot dead at the Parramatta Police Headquarters by 15-year-old Farhad Jabar who was killed by police at the scene in October.

On Wednesday afternoon New South Wales Deputy Commissioner Catherine Burn said a Guilford man, 20, has been charged with supporting a terrorist organisation and membership of a terrorist organisation.

"We will be alleging that the support that he gave was to facilitate the travel of the gunman's sister to Syria, the day before the murder of Mr Cheng," Deputy Commissioner Burn said at a press conference.

Detectives laid new charges on the three other men aged 23, 22 and 18, including membership of a terrorist organisation and conspiring to plan a terrorist attack.

The 23-year-old from Merrylands was already facing charges of acquiring a firearm without a licence, providing a firearm to an unauthorised person and involvement in a criminal group, among others.

The 22-year-old from Marsfield was already facing charges of involvement in supplying a firearm to an unauthorised person and participating in a criminal group.

The 18-year-old from Guildford was already facing charges of directing the activities of a criminal group and aiding a terrorist attack.

Deputy Commissioner Burn said it was "very important" to recognise the work of the state Joint Counter-Terrorism Team who "have worked tirelessly since October last year, under a very, very difficult circumstance, being the murder of a police colleague".

"The real significance is that this reflects the criminality of all of them involved to come together to actually prepare and plan to do an absolutely heinous criminal act which resulted in the murder of a police employee," Catherine Burn said.

The four will appear in Goulburn Local Court via videolink on Thursday and have been remanded in custody.