Zaid al-Hilli told ITV News that his family was "very encouraged" by the arrest made in the investigation into the death of his brother and his family.
"We are very encouraged by the recent developments. Hopefully we will get to the truth," he said.
But he added: "I don't want to raise my hopes."
More top news
The success of the No camp is mainly due to Tsipras convincing people a No vote will strengthen their hands in negotiations.
As we move into the weekend, expect things to get rather more unsettled weather-wise - thought it will stay hot and humid for some.
More than 80 prominent Britons, including Boris Johnson, Russell Brand and former Government ministers, urge Obama to release Aamer.