A "possessive, controlling" man killed two of his girlfriends five years apart, with their deaths recorded at the time as being caused by accidental or natural causes, a court heard.

Robert Trigg, 52, is accused of murdering 52-year-old Susan Nicholson, whose body was found on a sofa they had both slept on in Rowlands Road, Worthing, West Sussex, on April 17 2011.

Trigg is also charged with the manslaughter of another former girlfriend, Caroline Devlin, 35, who was found dead in bed on Mothers' Day by one of her children as they went to ask what she wanted for breakfast at home in Cranworth Road, Worthing, on March 26 2006.

Lewes Crown Court heard a post-mortem examination at the time recorded Ms Devlin's death as being caused by natural causes - an aneurysm - although there was "no physical finding" to support the conclusion.

In the case of Ms Nicholson's death, Trigg told emergency services she died after he accidentally rolled onto her in his sleep while they were on a sofa - a theory considered "plausible" after the post-mortem test was held at the time.

Prosecutor Duncan Atkinson QC said that when viewed in more depth, the circumstances of each death became different and "significant similarities" between each woman's death emerged.

Mr Atkinson said: "The prosecution case is that there is no coincidence here of two natural or accidental deaths.

"Rather, the prosecution case is each of Caroline Devlin and Susan Nicholson were unlawfully killed by the person common to their lives and to the death of each, namely this defendant."

Trigg, of Park Crescent, Worthing, denies murder and manslaughter.

The trial heard that after both causes of death were re-assessed by pathologist Dr Nathaniel Cary, he concluded Ms Nicholson was suffocated after having her head deliberately forced into the bed.

He also found that mother-of-four Ms Devlin's death was caused by a blow to the back of her head.

Jurors were told that both women had been subjected to violence during their relationships with Trigg.

"Indeed, inquiries have revealed that the defendant has a history of behaviour towards other women with whom he has been in a relationship that shows him to have behaved in a possessive, controlling and jealous way," Mr Atkinson said.

Following one alleged outburst of aggression by Trigg, Ms Devlin "prophetically" said: "I won't be here for my 40th," the court heard.

Jurors were told that Trigg did not call the emergency services following the deaths of both women.

His account of both fatalities "raised more questions than it answered", Mr Atkinson said.

On the night Ms Devlin died, one of her children heard the sounds of "rough and loud" sexual intercourse coming from their mother's loft bedroom.

The following morning, one of her other children went to ask Ms Devlin what she would like for her Mothering Sunday breakfast - and saw her naked body on the bed, but thought she was asleep.

Mr Atkinson said Trigg had left the house, but later returned looking "dazed and being weird" before asking one of Ms Devlin's children to look at their mother as she laid upside down in the bed with her head deep into the duvet. The alarm was then raised.

No CPR was attempted as Ms Devlin was already dead when medics arrived, the court heard.

Mr Atkinson said a number of police officers who attended believed her death was not suspicious.

"Clearly those officers were not in possession of the full picture now available, and the prosecution say that their opinion was incorrect," he said.

Neighbour Hannah Cooper said Ms Nicholson and Trigg had a "volatile and violent" relationship, with rows fuelled by alcohol and police being called at least six times following bust-ups between them.

In March 2011, Trigg was cautioned by police for battery relating to a row he had with Ms Nicholson who was punched in the face.

Mr Atkinson told jurors: "The question is whether this earlier incident assists you as to whether he had behaved aggressively towards her on the night that she died."

At 8.51am on April 17, Trigg called Ms Cooper and said: "It's Sue, I think she's dead."

Trigg's phone records showed he bought cigarettes from a nearby shop then called his brother Michael before phoning Ms Cooper who dialled 999, Mr Atkinson said.

He added: "At the time, as had occurred with Ms Devlin, the police treated the defendant as a bereaved partner rather than a suspect."

A pathologist at the time of Ms Nicholson's death found that Trigg's account that she died after he accidentally rolled onto her was a "possible explanation".

But in his review of the original pathology report, Dr Cary said: "It is very unlikely that someone asleep on a sofa with another could cause death in the manner proposed by simply rolling onto them."

Dr Cary had never come across a case of an adult overlaying in such a manner, and that he would not have expected this to happen between two adults.

He considered accidental airway obstruction to be the least likely possibility in Ms Nicholson's case.

And he concluded that his findings "most readily fit with enforced airway obstruction, potentially through a combination of the face being forced down into yielding material such as fabric... in combination with compression of the chest, giving rise to a rise in venous pressure".

Trigg was interviewed as a suspect in November last year.

Mr Atkinson highlighted similarities between the two cases, including the fact Trigg was in a relationship with both women at the time they died.

He also said Trigg and the women were intoxicated around the time they died, that both women died while he claimed they were asleep and that he did not dial 999 in either case after the women's bodies were found.

More than two years before Ms Devlin's death, Trigg was cautioned by police for common assault on a woman called Susan Holland in November 2003, jurors heard.

Trigg accused Ms Holland of sleeping with one of her neighbours, and he called police, telling them: "I'm going to kill her. You need to arrest me."

Neighbour and close friend Bridget Benger fought back tears as she recalled making a pact with Ms Devlin around three weeks before she died.

Ms Benger told jurors: "We made a pact that, because we were single parents, that if anything happened we would be there for each other's kids."

She added that Ms Devlin's personality changed noticeably after she started a relationship with Trigg.

Ms Benger said: "She became very withdrawn. She lost her spark and she seemed to drink a little bit more as well."

Ms Benger, who described Ms Devlin as a "lovely lady", recalled finding out about the discovery of her friend's body from Ms Devlin's eldest son who knocked on her door, telling her: "We can't wake mummy."

Trigg was at the bottom of the stairs and appeared "vacant" and Ms Devlin was found lying face down on the bed, she added.

Under cross-examination, Ms Benger also said Trigg seemed to care for Ms Devlin and was openly affectionate towards her.

The case continues.