Const. Brent Kelly said soon after he arrived to break up a scuffle between two brothers near Digby in July 2008, one man accused the other of sexually assaulting their sisters when they were young.
The one brother also told him the other man had impregnated a 14-year-old sibling in 1969, which was followed by the birth of a boy who still lived with the family, Kelly told the Supreme Court of Nova Scotia on Tuesday.
The Mountie said he was then told the family, whose identities are protected by a publication ban, had conspired at the time to blame the pregnancy on Barton, telling police the 19-year-old had broken into their house in Jordantown.
Based on the girl's testimony and that of her brother, Barton was later convicted of having sex with a female between the ages of 14 and 16. He was sentenced to probation for a year.
Kelly testified that DNA testing in late 2008 proved that the girl's brother was the father of her child.
"He was 1.9 million times more likely to be the father than anyone else," Kelly testified.
Dale Dunlop, Barton's lawyer, said court records show the brother was charged with indecent assault, but the charge was dismissed in 2009, though the reasons for that have been redacted from records.
In January 2011, the Nova Scotia Court of Appeal admitted the DNA evidence in Barton's reopened case, quashed his conviction and concluded he was the victim of a miscarriage of justice.
"I believe he had been convicted of something he hadn't committed," Kelly testified.
Barton, now 64, is suing the provincial Crown for malicious prosecution and the RCMP for negligent investigation.
Outside court, federal lawyer Angela Green dismissed Barton's claim.
"There's no evidence that any of the RCMP's investigation ... was in any way negligent," said Green.
The unusual case has been complicated by the fact that some court documents have disappeared over the years, including records that would confirm whether Barton actually stood trial.
Kelly testified that he couldn't find any records when he started looking into the case.
Barton testified Monday that he never gave a statement to police and never pleaded guilty to any charges, though the court documents say otherwise.
The RCMP officer who led the investigation into the allegations against Barton in 1969 testified Tuesday that he didn't remember the accused or taking a key statement from him.
Earl Hamilton, who retired in 1985, said he didn't remember any details of the Barton case until he had a look at the files that are available to the court, including a typewritten statement that he said was based on an interview he had with Barton in late 1969.
In the statement, used at Barton's preliminary inquiry, Hamilton quotes Barton admitting to having sex with the girl inside her home.
"I would have used his words when recording a statement," said Hamilton, now 84. "He told me that he had intercourse with (the girl) with her consent."
Barton testified earlier that the sexually explicit words in the statement were not his, saying he wouldn't have understood such terms when he was 19.
Hamilton also testified that before he took a statement from the girl, he asked people in the community to describe her character "to determine what kind of girl she was."
The retired inspector said it was standard procedure at the time to determine whether the accuser was promiscuous and how intelligent she was.
"You talked to anyone you could find," Hamilton said.
As well, Hamilton said that the girl indicated she had been violently raped by Barton, even though the charge that was eventually laid was a less serious offence, commonly known then as statutory rape.
"It's not rape as we know it," said Hamilton.