The alleged killer of Peter Falconio altered his appearance and made changes to his car after the Brighton backpacker's disappearance, a court heard.

A former girlfriend of murder suspect Bradley Murdoch said he shaved off his moustache and installed a new canopy on his Toyota Landcruiser when he returned home from an Australian Outback trip in mid-2001.

Murdoch was also sick for a week after returning from the journey, Beverley Allan recalled yesterday.

Ms Allan, 42, was giving evidence against her former lover at a committal hearing in Darwin, Australia, into the alleged murder of Mr Falconio beside an Outback Northern Territory highway on July 14, 2001.

Murdoch is also accused of the unlawful assault and deprivation of liberty of Mr Falconio's girlfriend Joanne Lees, 30, from Hove.

Earlier hearings revealed Miss Lees had two-timed Mr Falconio, 28, with another English backpacker named as Nick Riley, from Reading. The affair began after travel agent Miss Lees worked near Mr Riley, 30, in Sydney.

Fidgeting and smiling throughout her brief testimony yesterday, Ms Allan barely glanced at Murdoch as he sat in the dock on the other side of the room just yards away.

She told the court she started to "become close" to Murdoch, a customer at the Broome mechanic shop where she worked, in October 2000.

Ms Allan said: "(The relationship had) no pattern and no set days.

Prosecutor Rex Wild QC asked: "Was it a happy relationship?" She said: "Not really, I don't think."

Ms Allan told the court how Murdoch would regularly go on trips with his dog Jack in his Toyota for a week or more at a time, including visits to South Australia .

She recounted how, after one trip in mid-2001 - around the time Mr Falconio disappeared - Murdoch returned "fairly strung out".

He had been away for about a week. Ms Allan said: "He told me that it hadn't been a good trip. (He'd had) a few dramas.

"He believed someone was following him ... he had to find out who was following him."

Ms Allan said Murdoch was sick for about a week after returning from the trip, suffering from the flu.

He had also changed his appearance by shaving off his moustache and cutting his hair and then had work done to his Landcruiser.

She said: "He was clean-shaven, no moustache and he had just shaved his head."

Mr Falconio was believed to have been shot dead beside a remote section of the Outback Stuart Highway after stopping for a stranger.

His body has never been found.

The hearing continues.