Opening statements began Monday in the trial of a Burbank man accused of fatally stabbing his on-and-off girlfriend two years ago.

Stephen Joanou Jr., 27, is accused of killing Patrina Sabella, then 32, who was found dead behind a shed at South Weddington Park in Studio City with 20 stab wounds, prosecutors said.

Prosecutors said surveillance footage shows the pair buying coffee together at 7-Eleven in North Hollywood roughly three hours before she was found dead.

According to prosecutor Sharon Ransom, police found two coffee cups in the victim's car -- which was parked at the park -- and Sabella's DNA was recovered from one cup, while Joanou's was recovered from the other.

Joanou reportedly denied seeing Sabella that night to police, Ransom said.

Prosecutors argued that Joanou's DNA was recovered under the victim's fingernails, though Joanou's attorney Christopher Chaney argued that the amount was insignificant, consistent with standing or sitting in a car together.

The victim's father, Michael Sabella, testified Monday about the last time he saw his daughter on the night of March 19, 2012. According to his testimony, around 10:30 or 11 p.m., her daughter told him she was going to pick up Joanou, who did not have a car. He tried to convince her not to, but she went anyway, sneaking out of the house without saying goodbye, he testified. He said he was bothered by the couple's age difference -- he was 25 and she was 32 at the time.

Three hours later, he said, he got a call from police in North Hollywood informing him of what happened. 

Joanou reportedly returned home sometime between midnight and 2 a.m. without blood on his clothes and showing no signs that he had been in a physical altercation, Chaney argued.

"He was not upset or distraught," Chaney said.

Prosecutors said Patrina Sabella was killed shortly after midnight.

Chaney said his client was turning his life around, working in construction with his father after seeking rehabilitation for his drug problem.

Whoever committed the crime, Chaney argued, would have come home bloody, though no blood was discovered on his shoes or clothing.

No weapon was recovered, Chaney added.

-- Alene Tchekmedyian, alene.tchekmedyian@latimes.com

Follow on Google+ and on Twitter: @atchek.

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