A former American child actor is facing death penalty after admitting to three murders, including hurling a couple off their yacht after tying them to an anchor.

Skylar Deleon, 29, who starred in commercials as a child and had a bit-part role in Mighty Morphin Power Rangers film, is accused of killing the Arizona couple Tom and Jackie Hawks in 2004 in order to steal their boat.

He is also accused of killing another man, John Jarvi, from whom he allegedly stole tens of thousands of dollars in 2003.

In dramatic testimony given at the start of his trial in Santa Ana, California, his defence team embarked on an unusual strategy of conceding that he had committed the murders – but pleading not guilty on a technicality.

Gary Pohlson, his defence lawyer, said that – rather than seeing Deleon cleared of all charges – his main aim in defending his client was to prevent the death penalty being given out.

The court was told that the Hawkses took a cruise off Southern California thinking they were showing off their yacht, the Well Deserved, to an interested buyer and ended up pleading to be spared.

"The evidence is going to show that is how Tom and Jackie Hawks died, begging for their lives," Matt Murphy, the Orange county prosecutor, said. "The evidence is going to show Jackie Hawks was crying and saying ... I have a grandchild. Please don't kill me."

The prosecutor graphically described the killings. "Skylar threw the anchor overboard, the rope goes taut and it rips Tom and Jackie Hawks off that (boat)," he said.

Deleon, 29, is a former child actor who allegedly boasted that he was a star on the Mighty Morphin Power Rangers but apparently only had a small part in one episode.

Prosecutors say he meticulously planned to kill the Hawkses after learning they were planning to sell their 55ft (16.76-meter) yacht in November 2004 to spend more time with their baby grandson.

They say Deleon feigned interest in buying the nearly half-million-dollar yacht, then enlisted the help of two men to overpower the Hawkses on the ship before forcing them to sign over paperwork for the yacht and killing them.

Mr Murphy took jurors on a step-by-step outline of how the case unfolded after the Hawkses disappeared and family and friends began to frantically search for them around Newport Harbour, where they docked their boat.

He said that Deleon and his former wife, Jennifer Henderson, were a young couple saddled in debt and living in a converted garage, and had a bank account with only $2,619 two days before Deleon took the test cruise.

Henderson was convicted in 2006 of murder for her role in the deaths and was sentenced to two terms of life in prison without parole. Three other men have pleaded not guilty to murder and murder for financial gain and have yet to stand trial. One is expected to testify in Deleon’s case.

During this case, the jury will also consider the separate murder charge in the death of a man Deleon met in a work furlough program in 2003 while serving jail time for burglary.

Mr Murphy said Deleon got $50,000 from John Jarvi, then drove down to Mexico and slashed his throat and dumped his body before coming back.

The defence strategy stunned Ryan Hawks, Mr Hawks's 32-year-old son, who came to hear the testimony. "I was blown away," he said. "Thank God I was sitting down."

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