THE SUN was starting to set when Jean Newlove dropped the wreath gently into the sea at the place where her daughter Kirsty died. After a few moments, the ribbon bearing the phrase “Goodbye to an angel” unfurled and streamed out like a banner, and the riot of lilies and bird of paradise flowers bobbed on the surface.

Unable to lift her gaze from the wreath, Jean seemed to crumple. She gripped the side of the small boat and, for the first time since arriving on the Mexican island of Cozumel, let out a sob of anguish: “Kirsty, why did you have to die?” It is the cry of every bereaved parent, but there really are many unanswered questions surrounding the death of Kirsty MacColl, the award-winning singer and songwriter, on December 18, 2000. Kirsty was 41 when she was killed by the propeller of a speedboat as she dived with her two teenage sons off Cozumel. Afterwards, a 26-year-old boathand named Juan José Cen Yam told authorities that he had been driving, and last year he was found guilty of “culpable homicide”. He was sentenced to two years and ten months in prison, but was allowed to pay a £61 fine and go free.

But was Cen Yam, who can barely tell left from right, and who claims not to know what a knot is, really driving the boat? Jean Newlove doubts the official version of events, and despite failing eyesight and advanced years (she is 81), had come to Cozumel in search of the truth.

Unravelling the mystery of her daughter’s death was to be deeply distressing. “I heard for the first time in detail how Kirsty died, and it was much worse than I thought,” Jean said.

So traumatic was it for Iván Diaz, the 49-year-old instructor who oversaw Kirsty’s last dive, that he has given up his livelihood. He was an experienced divemaster, and Papa Hog’s, the dive shop he worked from, was recommended to Kirsty as an outfit that she could trust.

Kirsty was an experienced diver who had explored the reefs of Cozumel twice before. But she wanted to introduce her sons Jamie, 15, and Louis, 14, to the local reefs.

At lunchtime on December 18 they headed to the Chankanaab reef, which forms part of the National Marine Park of Cozumel and is one of the most popular dive sites off the Yucatán Peninsula. Kirsty and her sons, guided by Diaz, spent half an hour marvelling at a huge lobster, a massive eel and scores of fish and corals.

Diaz remembers what happened next in horrifying detail. “We had just come up to the surface and I was facing away from our support boat, the Scuba Shack. We were pretty close together, no more than a couple of metres apart. I turned round to signal to Manuel, our captain, and I saw this other boat coming right at us.”

The Percalito was only 400 yards away and, according to Diaz, was travelling at about 20 knots. It should have been able to swerve, but there seemed to be no one watching out. “It was going so quickly, I thought, ‘Oh my God, these guys are not going to change direction’. I called to Kirsty, ‘Look out!’ and tried to signal to this other boat, but it was going too quick.” Both the Scuba Shack and another dive boat, the Nazareno, tried to cut in front of the Percalito but it was going too fast. As the speedboat bore down on them, all Kirsty and Diaz could do was to try to protect her sons. “She pushed one of the boys out of the way and I grabbed the other one. Then it was on top of us.”

Diaz heard a clang, which was the sound of the propeller hitting Kirsty’s dive tank. She died almost immediately — post-mortem reports would reveal that her chest and leg were virtually severed. Both Diaz and Jamie were also hit, but not seriously injured. Surfacing, Diaz looked round and saw Kirsty floating face down.

It was Kirsty’s boyfriend, James, who had to break the news to her mother. “He called and said, ‘Jean, there’s been an accident and Kirsty’s dead’,” she recalls. Her son Hamish, Kirsty’s older brother, had a heart attack when he heard the news. Jean herself had to face not only her daughter’s death but the knowledge that her grandsons had almost died too.

After giving statements to the police, the boys returned to England with their father, the music producer Steve Lilywhite, who had flown from the US to be with them (he and Kirsty had divorced in 1995).

When her grandsons returned, Jean recalls one of them saying: “Granny, I’ll tell you all about it but only if you want me to.” Thus she began, slowly, to piece together what had happened that day. In time she learnt that not only was the boat that killed Kirsty speeding illegally, but that it wasn’t even supposed to be in the waters immediately around the reef. It was also true, however, that the divemaster had failed to put out a marker buoy and that although the dive boat was flaying a flag, it was not one that conformed to international regulations.