Ryan Sharp and his partner of 18 months, Deanne Struber, were arrested in April this year by officers attached to the NSW Police Fixated Persons Unit - a specialist squad set up in 2017 to target potential would-be terrorists or lone actors - after the pair used Facebook to track down the victims and "catfishing" style tactics to lure them into revealing their home address.

A set of agreed facts tendered to Wollongong Local Court on Wednesday said Struber was in the Macca's drive-thru at Warrawong on the afternoon of February 22 when she began reversing her vehicle, prompting the victims, who were in the car behind, to beep their horn.

Struber verbally abused the victims before driving off, however both vehicles stopped a short distance down the road and an altercation occurred.

Struber reported the matter to police and was able to obtain the male victim's name and suburb. She phoned Sharp who told her to look up the couple on social media. Struber discovered their joint Facebook page and sent Sharp a screenshot.

Sharp then created a fake Facebook account with an image of a young blonde woman and contacted the victims, inquiring about furniture they had listed for sale on Marketplace.

The victims provided Sharp with their address.

CCTV recorded Sharp attend the Koonawarra home early the next morning and smash up the couple's grey Ford Ranger with a baseball bat, causing about $10,000 damage.

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He then sent the pair a message threatening to set their car on fire and rape the female victim, saying "both of you have made a big mistake".

Two weeks later, Sharp again attended the couple's house, this time planting a bomb made up of sparklers, batteries and a circuit board under another vehicle at the premises. It detonated less than 90 minutes later.

When arrested, Sharp initially denied any involvement in the offences but later admitted to creating the explosive device. He claimed he only wanted to scare the couple, not hurt them.

He also admitted sending the Facebook posts, saying he was frustrated police hadn't acted on the road rage incident and had decided to take matters into his own hands.

In court on Wednesday, Sharp pleaded guilty to using a prohibited weapon and manufacturing a military style weapon. Several other charges, including two counts of intimidation, will be taken into account when Sharp is sentenced early next year.