The blast was one of seven events involving murders and bombings which were "inextricably linked" to disgruntled Family Court litigant Leonard Warwick, prosector Ken McKay said on Monday.

He was giving the crown closing address at the 73-year-old's NSW Supreme Court marathon trial.

The former firefighter has pleaded not guilty to four murders and 20 other offences related to the events which occurred between February 1980 and July 1985.

Justice Peter Garling began hearing the trial, without a jury, in May 2018.

Mr McKay said the seven events were inextricably linked to drawn-out Family Court proceedings involving Warwick and his ex-wife, Andrea Blanchard, which ran from 1979 to 1986.

Each event involved the "application of extreme violence, lethal or at least potentially lethal" events which were unique in Australia's history, the prosecutor said.

He referred to affidavits in which Ms Blanchard made claims against Warwick of physical assault, controlling behaviour and breaches of court orders.

"In our submission it doesn't really matter for Your Honour to determine the precise assertions," Mr McKay said.

If true, they revealed the considerable dispute between the parties and if untrue, they provided a motive for Warwick's anger with the system and his ex-wife's supporters.

Four events directly related to the Family Court hearings - the shooting murder of Justice David Opas, the bombing of Justice Richard Gee's home and of the Family Court building in Parramatta, and the bombing of the home of Justice Ray Watson in which his wife Pearl was killed.

These events were "book-ended" by events of serious violence which were related to Ms Blanchard - the shooting murder of her brother Stephen and a car bomb at the previous home of her solicitor.

The final event was a bomb which ripped apart a Jehovah's Witnesses hall, killing Mr Wykes and injuring 13 other members of the congregation offering support to Ms Blanchard.

"It is perhaps somewhat an impersonal way, a detached way to refer to them as 'events'," Mr McKay said, before giving personal details of the violence.

Joy Wykes testified her husband was sitting at the end of the row and they were holding hands.

Because it was quite a cold day, she had a little rug and placed it over their hands.

Her husband realised why she did it and whispered "I love you" and "that's when the bomb went off".

Mr McKay said the hall had been broken into through a window on the morning the bomb went off under the stage. It had also been broken into a week earlier.

The prosecutor submitted the judge would find that human blood, type O positive, was found on cardboard and carpet in the hall.

"The accused's blood group was O positive," he said.

Mr McKay will continue his address on Tuesday.

Australian Associated Press