Kingsley decided to leave all talk about Voldemort for now; it was far above his pay grade and he had no way to validate anything this man was saying without going to Dumbledore. Besides, his focus at the moment was the cult that 'Regulus Black' claimed he had information about. It wouldn't hurt ot hear the man out, check on his sources, and follow this line of investigation to the end.
"How many, exactly?" Kingsley had a good idea of the number of wizards involved, and if 'Regulus' numbers were close to his estimation, then he'd at least hear the man all the way out. "So, we're talking about this going back, what? Eight or nine years?" The earliest unsolved murders he'd been able to trace to the cult dated from 1979, so that would pan out if it were the case. He'd also made the connection to the Death Eaters himself, so not much of what 'Regulus' had was of any use to him.
He eyed the young man. "You're not giving me anything I hadn't already pieced together for myself," he said. "Give me names, and we'll see how they pan out. Then we'll talk about what sort of deal you can make for the information." He didn't for a minute think that this man was innocent of any participation in the rituals and murders, but they'd made deals with criminals before, in the name of the greater good. If he could take down the whole cult, letting one man off would be a decent compromise.
"In the mean time, you'll be placed under protective custody until your claims can be verified."