(Cover) - EN Showbiz - Moby has tweeted about his sorrow over the death of Amy Winehouse saying he wished he had "been able to help her".

The American DJ headlined the June 18 show at Belgrade's Tuborg festival where the singer slurred her way through the set and was booed by the 20,000-strong audience.

He took to his Twitter page after hearing the 27-year-old had been found dead at her home in North London on Saturday after a long battle with drugs and alcohol.

"After our show in Serbia I wish I'd been able to help Amy. I'm sorry," Moby posted.

He told the Hollywood Reporter that the moment he got out of his car for the concert he "knew something was wrong" and could hear the audience booing "louder than the music".

"She was on stage for about 30 minutes, then she left and was lying down on a flight case backstage surrounded by some people," Moby said. "I was horrified."

Moby has been sober himself for several years and said he "naively and presumptuously" hoped to speak to her before or after the show to see how she was doing after her recent stint in rehab.

He said he understood Amy's "love of drinking and using drugs and existing in a chemically altered state of consciousness" but had been hopeful she would get better and had "resigned sadness" about her passing.

Meanwhile, Katy Perry has said the death of the Back to Black singer has made her even more grateful that her husband Russell Brand, a former drug addict, is now sober.

"My heart felt really sad," Katy said on Good Morning America about Amy's death.

"My husband has been clean and sober for almost nine years. I see him working a program and working on himself every single day.

"It gave me a real gratefulness for my husband who got clean when he was 27."

Russell has written a lengthy tribute to his friend saying that addiction should be treated as a disease that is potentially fatal and called Amy "sweet and peculiar but most of all vulnerable".

Earlier today Amy's father Mitch, mother Janis, brother Alex and on/off boyfriend Reg Traviss went to her Camden home where fans of the singer have built a shrine.

At the moment police are treating her death as unexplained but not suspicious. A post mortem took place in London earlier today and was deemed inconclusive.

Since no cause of death has been determined, Sky News sources claim officials are awaiting the results from toxicology tests to find out exactly how and why Amy died. The results of the tests are not expected for another two to four weeks. (C) Cover Media