、。
It seems he was struck with some heavy weapon — his skull was shattered.
Literal
Something heavy weapon [with-で] was-done [seems-らしく], skull [topic-は] was-shattered.
Evidential ~らしい in its adverbial/conjunctive form ~らしく links the inferred cause to the stated effect. ~らしい marks information the speaker is reporting as a secondhand conclusion — 'it seems/appears,' 'from what I can tell.' やられる is the passive of やる, colloquially used to mean 'be done in,' 'be attacked,' 'get hit,' with an unavoidably adversarial nuance. The sentence splits the event into two views: inference first (it seems he was hit by a heavy weapon), then observed result (the skull was shattered) — typical of forensic/investigative narration.