We know enough about trolls to realise that they are not a uniform bunch of internet thugs and it is unwise to lump them into one category of nastiness.

There are the wicked, the criminal, the drunk, the disinhibited, the sad, the obsessives. Early this month, the pitiful case of Brenda Leyland, who was found dead in a Leicester hotel soon after being unmasked as a remorseless online abuser of Kate and Gerry McCann, overturned even the broadest understanding of what the constituency of trolling really is.

There is an incontinent sort of viciousness that goes with attacking people from the anonymity of a Twitter account. No-one in the neat village of Burton Overy, Leicestershire, suspected Mrs Leyland had a cruel bone in her body, let alone the sort of mindset to pursue a vitriolic campaign again the grieving parents of the missing child, Madeleine McCann.

A likeable, churchgoing woman of no obviously strong views, she seemed more interested in gardening, photography and quizzes than any solitary obsession with tweeting. She also had a passionate, innocuous leading role in the village's annual scarecrow competition.

Yet, hiding behind the alias @sweepyface, she insinuated that the McCanns were implicated in their three-year-old daughter's disappearance during a family holiday in Portugal in 2007 - a theme that had obsessed her for four years. According to the website BuzzFeed, she was sometimes posting more than 50 tweets a day, even on Christmas Eve, from 7am until midnight.

She claimed the McCanns were trying to silence their critics. The accusations were not original but her turn of phrase was blithe and deadly. "You will be hated for the rest of your miserable, evil, conniving lives, have a nice day!"

When Mrs Leyland was confronted by Sky News about her campaign of hate, her vituperation shrivelled like a pricked balloon. She mumbled about being entitled to say such things and said she hoped she had not broken the law. Soon after, she went to ground. Now she is dead. It looks certain that the two events are connected and that she could not live with the ignominy of being a named troll, suddenly outed, suddenly herself the target of torrents of abuse.

Brenda Leyland, nee Shevlin, was born in Stockport, Lancashire, the daughter of Colin Shevlin, a squadron leader in the RAF, and his wife, Doreen. As a girl, she had attended the Convent of the Immaculate Heart of Mary in West Sussex, and studied at Goldsmith's College, London University. Her marriage to Michael Leyland, a company director, ended around 2000 and he remarried in 2002.

To say that Mrs Leyland, a 63-year-old divorcee with two grown-up sons, did not conform to the image of the half-literate troller who spits poison as a reflex compensation for lack of self-esteem, is an understatement. She fitted well, if unobtrusively, into the village life of Burton Overy. She was outwardly sociable, with an element of loneliness and disappointment in her life that had intensified with age and the breakup of her marriage - and she developed such an obsession with the McCanns that almost all the 4625 tweets she sent from December 2010 were about the case, many taking issue with their supporters.

It was an industrious hidden life. Emboldened by disguise, she shared the assumption of all internet trolls that she could say anything she pleased without being held accountable. As Professor Mary Beard told the London Daily Telegraph when she was campaigning last year against misogynist trolling: "Anonymity has disguised the nature of authorship. It has allowed these evanescent creatures on the web to blast off without thinking of the victims. Somehow no-one in this conversation is real. They are just names."

Mrs Leyland tweeted triumphantly at the height of her persecution: "You can move to France, anywhere, but social media is everywhere! Our memories are long, Maddie deserves it."

Her message seemed mild compared with some of the foul-mouthed stuff that has continued to rain down on the McCanns - but there was menace in it, too. Questioned by Sky News reporter Martin Brunt, she said she was "entitled" to tweet as she did - though her justification, without the protective cloak of anonymity, sounded far from confident.

Brunt, one of the most respected television reporters in the business, was invited into Mrs Leyland's house and spent time talking to her about her concerns over the McCann case off-camera. Inevitably, he has himself now become the victim of trolling, with a Facebook page set up under the title "Sack Martin Brunt".

What he could not have known when he approached her was the personal tragedy behind Mrs Leyland's confessed obsession. She was estranged from her eldest son, Daniel, and never spoke of him. Saturday, the day when her body was found in Leicester's Marriott hotel, was Daniel's 37th birthday.

A neighbour said: "Deep down it must have hurt that he cut his mum out of his life. Whether that made her anti the McCanns, who seemed to have a very loving, supportive and happy family, we will never know. We were friends but grew apart, she was a one-way ticket. She could be quite nasty and controlling.

"When Madeleine first went missing she used to go over to her home village all the time. She used to go to the local pub and the shops telling everyone what she thought about the family. It seemed very odd behaviour."

Mrs Leyland's younger son, Ben, 30, lives in Los Angeles where he works for a law firm. He posted a brief emotional tribute on Facebook saying: "I love you mum and I will miss you forever. I am love and I am light, thanks to you."

In the absence of the one person who seemed to value her, such village friendships as she had sound poor substitutes for meaningful family life. Mrs Leyland's mother died in 2004 and she had distant relations in Australia, but few in Britain, other than her estranged son. A friend described her as "lonely beyond belief".

A neighbour in Burton Overy whose son is a friend of Mrs Leyland's son, Ben, said: "I just can't understand why she would have posted those things. No-one in this village can. But then, for her to take her life is even more inexplicable. She just packed her bags and took off."

Another villager suggested the threat of being unmasked and prosecuted was overwhelming.

"She was a proud, very bright articulate and upstanding lady and the thought of a prison sentence hanging over her would have devastated her. Sadly, she couldn't live with herself."

London Daily Telegraph