The court found him not guilty of the murder charge.
Literal
Court [topic-は] his [possessive-の] that murder charge [concerning-について], not-guilty-[quotative-と] judged
について ('concerning, regarding, about') scopes the charge. 無罪とする means 'to rule (someone) not guilty' — the と is quotative, marking 無罪 as the verdict being assigned. Its opposite is 有罪とする (rule guilty).