That didn't seem to have precluded the prosecution of Swartz. I'm skeptical that any complaint actually needs to be filed. I'm pretty sure that the FBI can investigate and the DoJ can prosecute without one.

IMO an analogous situation would be where a police officer acts to prevent a in-progress burglary he has stumbled across even in the absence of a complaint by the owner of the property that's being burgled.

EDIT: Or -for the sticklers out there- another one would be prosecutors pursuing an attempted homicide case despite the fact that the intended victim declined to either press charges or even complain to authorities about the attempted slaying.

In the Schwartz case, MIT's network security reported the "intrusion" to Cambridge Police and they brought in the US Secret Service who then contacted the DOJ.

I'm not saying somebody has to press charges, that's not how it works, but the police have to be aware of the supposed crime.