An award-winning teacher hacked her husband to death, went to school the next morning to teach her class of nine-year-olds, then bought some bleach on her way home to clean up the blood, police in the Detroit area alleged last week.

The murder, in a luxury gated community in America’s third-wealthiest municipality, “was the most gruesome homicide I’ve seen in 40 years of law enforcement, including 22 years in Detroit, America’s most violent city”, Farmington Hills police chief William Dwyer told The TES.

Robert Seaman, 50, who sustained a bludgeoned skull and fractured clavicle was stabbed 20 times and had his throat cut while he was still alive, the post-mortem report found. At Longacre elementary school the next day, Nancy Seaman, 52, appeared “dishevelled”, and out of sorts, Mr Dwyer said.

The estranged couple had a violent row on May 9, and Mrs Seaman stormed out of their sprawling $500,000 (pound;272,000) mock-Tudor home. Minutes later she was caught on camera at a local hardware store buying the hatchet used for the murder, Mr Dwyer said.

She returned to the same shop after school the next day to buy cleaning materials, a tarpaulin and some insulating tape. Her husband’s body was found bound up in the tarpaulin two days later. Detectives, acting on a tip-off, noticed “something resembling a mummy” in the back of the couple’s car.

Mrs Seaman has pleaded not guilty to first-degree murder. Her lawyer said that she was a battered wife, who had suffered years of physical abuse at her husband’s hands. A preliminary hearing is set for June 23.

The killing has rocked the exclusive Detroit suburb of Farmington Hills.

Mrs Seaman was a popular colleague at Longacre elementary and had won several awards for teaching excellence from the local education authority.

“People were very surprised and quite upset,” said Estralee Michaelson, director of Farmington Hills school district’s “Safe Schools” initiative.

Trauma counselling has been laid on for fellow staff and students.