Well, they were apparently being abused by their family, had applied unsuccessfully for asylum, and were (or thought they were) about to be deported to Saudi Arabia. They had told people that they would kill themselves if they were forced to go back. They had spent weeks maxing out their credit cards staying in luxury hotels and shopping. They had run out of money the day before they died, and were seen hours before their bodies were found at a park on the bank of the river praying. Also they weren't bound in any way that would have caused them to drown - they had apparently taped themselves together, possibly to keep their bodies from floating apart.
I mean, it's possible that they were murdered. But it's not unreasonable to conclude from the available facts that it was suicide. Do you have access to additional facts that would dispute that conclusion?