The Tamil Tigers, outlawed in Sri Lanka, battled with the Sri Lankan government for three decades until they were crushed in 2009.
Police arrested Thambithurai, 46, in this Pacific coast metropolis in early 2008. He was released on bail days later.
Sentencing is scheduled for Friday, with the maximum penalty 10 years in prison.
In court on Tuesday the prosecutor recommended a two-year jail term, while defense lawyer Kathleen Bradley asked for a three-year conditional sentence.
Fund-raising for the LTTE's cause was banned under terrorism laws in many countries, and they have been successfully prosecuted for 27 years in Italy, Germany, France and Australia for collecting a "war tax" from expatriates, said terrorism expert John Thompson of