A lengthy inquest has been re-examining the mysterious death of the 17-year-old, whose body was found on the tracks south of Tamworth, in northern NSW, 37 years ago.
An initial police investigation determined the Gomeroi teenager wandered onto the tracks either deliberately or in a dazed state, something his family has never believed.
Rumours have long lingered that several Tamworth locals had something to do with Mr Haines' death, including his close friend Glenn Mannion, the inquest has been told.
There were theories that Mr Mannion - who worked at a service station - was linked to a stolen Torana found crashed near the tracks in the early hours of January 16, 1988.
Mr Mannion's former girlfriend also gave evidence that he divulged specifics about Mr Haines' death, including that a towel was under his head and his body was covered by a cardboard box.
But Mr Mannion denied those accusations.
"I have no idea what happened to Mark or how he ended up out there," Mr Mannion told the NSW Coroners Court in Lidcombe, western Sydney, on Monday morning.
"100 per cent, absolutely, it was not me."
A coroner returned open findings in 1989 over the death.
The new inquest came after a long campaign from Mr Haines' uncle Don Craigie, who took part in a traditional smoking ceremony outside court as Deputy State Coroner Harriet Grahame watched.
The barrister representing Mr Craigie at the inquest, Jalal Razi, asked why Mr Mannion's answers to police and the inquest were short or incomplete.
"The answers are the answers," Mr Mannion replied.
Mr Mannion moved away from Tamworth for work soon after Mr Haines' death, but he denied the two events were linked.
"Can you see ... that might give the impression to the family that you were trying to run away?" Mr Razi asked.
"If that's what they believe, that's what they believe," Mr Mannion said.
He later addressed Mr Craigie directly from the witness box, saying he hoped answers were found.
Opening the final hearings, counsel assisting. Chris McGorey, described the hours before and after Mr Haines' death.
A crew driving a goods train from Werris Creek station to West Tamworth on January 16 noticed what appeared to be a white box on the tracks, Mr McGorey said.
When they travelled back to the site on a different train about 15 minutes later, the driver caught a "fleeting" glimpse of a body.
Emergency services soon found Mr Haines' body with a towel or blanket under his head.
"A number of questions have arisen over the past 37 years," Mr McGorey said.
He said the coroner may consider questions including how and why Mr Haines came to be on the tracks, who may have been with him at the time and which of the trains hit him.
The hearings are due to run into Friday.
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