Kelvin Mercer choked unconscious a colleague at the PPCS plant in Mosgiel two months before killing his estranged wife and six-month-old son, a work colleague claimed on television last night.
PPCS worker Don Miller told Holmes that Mercer had undergone an anger management programme after the incident.
Mercer's actions - placing hisvictim in a "sleeper hold" until he passed out - had left his victim unconscious for about 30 seconds, Mr Miller said.
"He knew he did wrong; he even admitted he did, and he went to anger management over it," Mr Miller said.
Mercer had arrived for work early last Thursday morning distraught, and had confessed to "keying" the car that belonged to Wendy Mercer's new boyfriend, Mr Miller said.
About 6am, he had broken down and confessed he felt like going to Mrs Mercer's Ettrick St home and "smashing their heads in". After trying to reason with him, Mr Miller sent Mercer home with advice to seek help.
Just over an hour later, Mercer was pulled badly burned, but at that stage still alive, from the home that also contained the bodies of Mrs Mercer and baby Will.
Mercer suffered burns to 40 per cent of his body and died at Middlemore Hospital in Otahuhu early on Saturday.
Mr Miller said Mercer had never spoken badly of his estranged wife, despite disputes over custody and visiting rights for his children.
He had been a regular user of marijuana, but had all but given up using the drug.
"I think there's more to this than just a jealous ex-husband," Mr Miller said.
"There's only two people that know what happened but, sadly enough, they are not going to be here, ever."
Police said yesterday that they might never know exactly what happened in the Mercer home if doctors oppose interviewing the two young survivors.
Aurial Mercer, 5, and her 3-year-old sister, Crystalynn, are being cared for by relatives following their discharge from Dunedin Hospital, where they were taken with knife wounds last Thursday, the day their mother and baby brother were murdered.
Detective Senior Sergeant Tony Wakelin said that although the sisters were the only surviving witnesses, they would not be interviewed if doing so would be detrimental to their recovery.
A trust fund has been organised for the two young girls by Otago Kindergarten Association general manager Andrew Campbell-Stokes.
Donations can be made at any National Bank branch or Dunedin kindergarten.
