By 2006 the investors became restless about their money. Calls, emails and meetings were attempted with Rens.
When they eventually received responses from him some of them asked for their money back, Mr Lucas said.
In 2007, Rens left his Havelock North home "without telling any of the investors where he was going" and without any money being returned, and not long afterwards police were notified.
Rens was arrested and charged in 2010.
Rens' defence lawyer Bill Calver told the court the single issue was if Rens had intentionally failed to account for the funds.
"You'll hear during this trial how the accused has been incredibly frustrated about finding where the money went, he'd like nothing more than to account to everybody for their money," Mr Calver said.
"He hasn't been able to ascertain what happened to the money. The defence is that he is not a crook at all."
The first investor, club flying instructor James Foreman, took the stand yesterday.
The court heard how he wrote a cheque of $5000 to Rens in October 2004. Two other $3000 payments followed.
Mr Foreman said he believed it would be invested through an off-shore company, based in the Caribbean, which he understood was because of tax laws.
Mr Foreman said that when some investors starting asking for their money back, they received "all sorts of excuses".
These included that the accountants, based in Uruguay, didn't work around the December-January period and Rens was having trouble transferring money from bank to bank, Mr Foreman said.
"It became apparent after a while that people were getting told different things by Peter ... the explanations weren't consistent."
The trial is expected to continue today.