The closing submissions for the case against Thomas Validakis, 30, were heard in Wollongong Local Court on Monday where he has plead not guilty to intimidating his former partner and letting off the explosive device inside the unit block on Virginia Street, North Wollongong on November 5, 2018.

In court, police prosecutor Sergeant Sean Thackray alleged that Validakis sent his ex-girlfriend more than 100 messages to her phone, that she changed multiple times in a bid to stop contact after they broke up.

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Then after she continued to reject him and started a relationship with another man, Validakis found out where she lived, made the device, placed it near her door before it detonated in a targeted revenge attack, Sgt Thackray alleged.

He said Validakis' DNA was detected on four pieces of the firecracker found in the stairwell and alleged that was transferred when Validakis "rubbed his hands over it when making it".

Sgt Thackray alleged Validakis sent messages, some of which threatened the ex-girlfriend including one that said "watch your back", and had previously burnt some of her property.

The police prosecutor also alleged the ex-girlfriend saw, from her balcony, Validakis come to her unit block a week prior to the explosion.

Validakis' defence lawyer Matt Russoniello said the case against his client was "circumstantial".

He said there were no witnesses the prosecution produced that placed Validakis at the scene on the day of the explosion nor that there was evidence the former girlfriend was the intended target of the explosion.

Mr Russoniello claimed the DNA evidence was "inconclusive" as Validakis' DNA could have gotten onto the firecracker through secondary transfer.

The lawyer labelled the text messages sent by Validakis to his ex-girlfriend as "annoying" and "unwelcome" but claimed they were not intimidating as the prosecution suggested.

Mr Russoniello also claimed the girlfriend did not report the burning of the property and the visit to her apartment to police, nor did she take out an apprehended violence order against Valiakis.

Magistrate Jillian Kiely adjourned the case to September 4 to consider her judgement.

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