Shawkey, 47, has pleaded not guilty and maintains that he believes Robert Vendrick, 71, is living somewhere in Mexico.
Vendrick vanished in 2008 and his body has never been found. His one-time business partner is standing trial for murder. Opening arguments began in Santa Ana.
"Mr. Shawkey is a con man with complete disregard for the value of human life," said Orange County Deputy District Attorney Ebrahim Baytieh.
Prosecutors said Shawkey, 47, swindled Vendrick out of $1 million in an investment scheme. When Vendrick demanded his money back, prosecutors allege Shawkey took him out on a boat and threw him overboard.
Baytieh alleges Shawkey took more than $1 million from Vendrick beginning in 2004 when they met online through business ventures.
"Not a single investment returned money," said Baytieh.
Tuesday jurors heard how by 2008, Vendrick was in financial trouble with $100,000 in credit card bills. His retirement money was gone and his wife was demanding the money back.
The prosecution alleges that Shawkey lured Vendrick on a boat after lying about a trip to San Clemente Island to close a secret government deal. He got Vendrick to give him $100,000; $40,000 came from Vendrick's brother, Fred.
Tuesday jurors watched surveillance video of Vendrick and Shawkey leaving Dana Point on February 16, 2008, the last time Vendrick was seen.
Shawkey tells investigators he and Vendrick took a boat ride, but Vendrick became uncomfortable and asked to return to Dana Point, claiming he would meet him later. The prosecutor alleges Shawkey threw Vendrick overboard.
The prosecution alleges Shawkey eventually went to Long Beach, where he tried to withdraw Vendrick's recently deposited money. Shawkey told investigators several stories of where Vendrick could be, including various cities in Mexico.
"Mr. Vendrick had a lot of secrets and lies and he chose not to tell," said Shawkey's defense attorney, Brian Waite.
Vendrick was a retired man from Phoenix who had worked in the software industry. Prosecutors say Vendrick met Shawkey online several years ago. Shawkey corresponded with him via email until finally, Vendrick trusted him with hundreds of thousands of dollars to put toward a software development plan.
Prosecutors say there was never any software development plan in the works.