Complex sentence: An earlier probe by the US military had said that 20--30 civilians were killed along with 60--65 insurgents and an only partially released American inquiry said "no one will ever be able conclusively to determine the number of civilian casualties that occurred".
Split into simpler sentences: An earlier probe by the US military had said that 20--30 civilians were killed along with 60--65 insurgents. A partially released American inquiry stated "no one will ever be able conclusively to determine the number of civilian casualties that occurred".