A 15-year-old Muslim teenager who shot dead Sydney police employee Curtis Cheng was found with a bloodstained suicide note on his body.

The note found on Farhad Jabar outside the NSW Police Force headquarters in Parramatta, Western Sydney, read 'I have come to put terror in your hearts'.

It also said 'an act that will cause nightmares during the night-time and hell during the daytime' and a reference to this being 'the world of Allah'.

The first half of the bloodstained note found on Farhad Jabar's body outside the NSW Police Force headquarters

The second half of the bloodstained note found on Farhad Jabar's body outside the NSW Police Force headquarters in Parramatta, Western Sydney

Farhad Jabar, (pictured), shot dead police employee Curtis Cheng on the afternoon of October 2, 2015

The full note found on Farhad Jabar outside the Police Force headquarters

Jabar allegedly supplied the gun used to kill NSW Police employee Mr Cheng originally obtained the 'wrong' weapon, a Sydney court has heard.

Police surveillance material played at a committal hearing in the Downing Centre Local Court on Monday allegedly shows the terror plotters encountered a major glitch in their plan just hours before Mr Cheng was shot dead on the afternoon of October 2, 2015.

Farhad Jabar (pictured) gave an Islamic State salute to a security camera in a mosque before the shooting

Aerial police footage allegedly shows Talal Alameddine, 24, arranging to supply the murder weapon to fellow accused terror plotter Raban Alou, 19, at a rendezvous at a park at Mays Hill, near Parramatta, about 1.30pm on October 2.

In audio from Alou's car that was played to the court, Alou can be heard saying, 'What did you bring?' and Alameddine replying, 'Well, I brought the 30 cal, bro.... You wanted the big one.'

A displeased-sounding Alou can be heard saying, 'S*** bro.'

Crown prosecutor Paul McGuire SC says Alameddine had provided 'a firearm that turns out to be not the firearm that's requested due to the wrong type or the wrong size'.

Surveillance footage shows Alameddine and Alou then driving to Merrylands, where Alameddine lived, allegedly to obtain the right weapon.

The men were followed by a second car carrying another accused terror plotter, Mustafa Dirani.

Mr McGuire said the revolver used to kill Mr Cheng was a .38 calibre Smith & Wesson, which is relatively small and easily concealed compared with the .30 calibre gun that was originally supplied.

Alameddine, Alou and Dirani are all accused of supplying the gun used by 15-year-old Farhad Jabar to kill Mr Cheng outside Parramatta police headquarters about 4.30pm that Friday afternoon.

Jabar was shot dead by police in an exchange of gunfire shortly after.

CCTV footage shows he prayed at a Parramatta mosque and gave the Islamic State salute to a security camera there before he went on foot to shoot Mr Cheng outside the headquarters.

15-year-old Jabar caught on CCTV footage believed to be raising his finger as an Islamic State salute at the mosque

The teenage boy who shot dead Sydney police employee Curtis Cheng gave an ISIS salute to a security camera at a Parramatta mosque (pictured) before carrying out the murder

'The raising of the index finger has become known as the IS salute,' Crown prosecutor Paul McGuire SC told the Downing Centre Local Court on Monday

Crown prosecutor Paul McGuire SC said just before the 15-year-old left the mosque for the police station, he could be seen raising his index finger and looking at the mosque security camera.

'The raising of the index finger has become known as the IS salute,' Mr McGuire told the Downing Centre Local Court on Monday.

The footage shows Jabar praying at the mosque before striding through the streets of Parramatta in Islamic robes with a Nike backpack on his back, on his way to shoot Mr Cheng.

Mr McGuire said the bloodstained suicide note was almost identical to a torn-up note found in a bin in Jabar's bedroom that appeared to have been written by his sister.

Jabar's sister allegedly flew to Syria the day before Mr Cheng's murder.

Mr Cheng (far left) was shot dead by Farhad Jabar, 15, outside the police HQ in Parramatta in February 2015, where he worked as an accountant

After carrying out the murder of Mr Cheng, Farhad Jabar was shot by police in an exchange of gunfire

On a bloodstained note found on his body outside the police HQ the teen had scrawled that his was 'an act that will cause nightmares during the night-time and hell during the daytime'

Mr McGuire said that after Jabar shot Mr Cheng, the online Islamic State magazine Dabiq referred to the teenager as among the 'brave knights' of jihad who had 'struck the crusaders of Australia and killed one of their personnel'.

'The Crown says that reference ... establishes that the Islamic State was taking credit for the act of terror that was committed by (Farhad Jabar),' Mr McGuire said.

Talal Alameddine, Mustafa Dirani and Milad Atai are facing a committal hearing accused of aiding Jabar's plot.

Raban Alou is also accused over the plot but is not involved in Monday's committal proceedings.