You have to take the "killer" to the other side.
then head back to the "Suspect" and the "Brother". Now take the
"Brother" and take him to the other side of the river.
When your there take the "Killer" back to the "Suspect" when your there
take the "Suspect" and bring him to the "Brother"
now the "Brother" and the "Suspect" are together on the right side of
the river you only have to bring the "Killer" to the other side and your
finished.
WARNING!!!:
DON'T MAKE ANY MISTAKES BECAUSE YOU MAY ONLY TAKE SEVEN TRIPS TOTAL!!!