Headteacher Emma Pattison was arrested after a domestic row with her husband seven years ago.
Just before midnight George Pattison called police claiming she had assaulted him at their home. He said his wife had slapped him around the face.
Two minutes later, he rang again to ask officers not to come because it was a trivial matter and he had overreacted.
But police did go to their home in Caterham, Surrey, and arrested Mrs Pattison on suspicion of common assault. She was questioned in the early hours, with a solicitor present, but was later released without charge.
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Police were told that the couple were having marital problems and were getting counselling to try to overcome them. One of the issues was Mrs Pattison’s job. She was deputy headteacher at an independent secondary school in Leatherhead.
Early on Sunday, the couple and their seven-year-old daughter Lettie were found shot dead at their new home at Epsom College, the independent school where Mrs Pattison became headteacher in September.
Mrs Pattison, 45, had earlier made a distressed call to a relative, but by the time family members arrived all three were dead.
Police launched a homicide investigation and believe Mr Pattison, 39, shot his wife and daughter before killing himself. His legally-owned shotgun was found nearby.
Two days earlier, police had called Mr Pattison to check his new address, a requirement under the shotgun licensing laws. It is understood police raised no objection, but they later reported the brief telephone contact with Mr Pattison to the Independent Office for Police Conduct (IOPC) to investigate any potential misconduct or breach of policy.
Police also told the IOPC of the arrest of Mrs Pattison and their handling of that investigation in May 2016.
Epsom College has been shut all week and is not expected to re-open until after the half-term holiday.
Acting headteacher Paul Williams told parents in a letter: “Now is a time for families to come together and try and process this shocking news.
“The impact on your children cannot be underestimated and we are doing everything we possibly can to support them in whatever way they need.”
Security guards were on the gates of the college, where full boarding pupils pay more than £42,000 a year.
The independent secondary school was founded in 1853 to provide education for the children of poor members of the medical profession.
Surrey police refused to discuss Mrs Pattison’s arrest in 2016.
The results of autopsies on the bodies of the couple and their daughter are expected by the end of the week.
