Callous drug addict Jason Caswell injected his girlfriend with a fatal dose of heroin because she was 'moody' and he wanted to shut her up.

Tracey Bradley, 28, had been trying to kick the destructive habit and regain custody of her seven-year-old son, a Court was told.

In a heroin session with fellow addicts the day before her own death, Miss Bradley had injected alcoholic Christopher Wilson, causing him to suffer a fatal overdose. Bradford Crown Court was told Miss Bradley was deeply upset by the tragedy and had confided in drugs workers about the incident hours before Caswell, tired with her bad mood, gave her the fatal fix.

Handing Caswell, 29, a four-and-half-year sentence, Judge Alistair McCallum highlighted the massive risk users faced every time they pushed needles into their bodies.

Judge McCallum said: "I'm satisfied that you injected part of a wrap of heroin that you acquired some time during that night and, as you told me yourself, you had absolutely no idea what that substance was." Det Supt Phil Sedgwick, who headed the case, echoed his view, adding: "When people buy heroin, they have no idea what they are buying or how strong it is.

"It is not like going to the supermarket and buying a branded product with the ingredients listed clearly on the back. You do not get a guarantee with them."

He added: "Dealers will mix the drug with all sorts of substances to improve their profit margins and this sometimes includes things such as brick dust or strychnine."

Det Supt Sedgwick added that, when mixing intakes of alcohol and heroin, it only took a small amount of each substance to prove deadly. And if someone were accustomed to taking heroin of low purity, a powerful batch could cause them to overdose and die.

Throughout the week-long trial, Caswell, of Hainworth Wood Road, Woodhouse, Keighley, had denied manslaughter, insisting that Miss Bradley had taken the drug herself.

But, after hearing how he admitted to a nurse giving the injection, only to change his story when interviewed by police, a jury found him guilty by a 10-2 majority.