Antonin shook his head, "Inside the wards means family or close friends. The younger brother would be almost too convenient a suspect in times other than these."
"Most Durmstrang students take the Introduction to the Dark Arts course. It would be simple to contact the headmaster's office for a list of the subjects the younger Montague took. The problem arises if he's had off-the-record instructions - which is more than likely if one of the more exotic Dark attack spells was used." He shrugged, "We both know there are less than ethical practitioners of the Old Magic out there. Few of them have actually bothered to become registered as Masters of the Dark Arts."
Antonin went on, "I'll contact Durmstrang in the morning, officially, and also off the record to a few of my old professors and see what they have to say about Guilian Montague."
"Dark attack spells aren't really my area of study, but I'd be more than happy to take a look at Damian Montague if it might do any good. Do you have any indication of what spell was used? For that matter, what were the effects?"