The police are investigating the identity of the attacker.
ネットワークへの攻撃者は特定されていない。
The attacker on the network has not been identified.
襲撃者 implies a sudden raid or assault, often with a connotation of surprise, whereas 攻撃者 is a more general term for an attacker.
Compound of 攻撃 (kōgeki, 'attack') and 者 (sha, 'person').