"Does it matter, Sirius? I can't prove anything either way. He's right. Dumbledore could find out any secret within this castle. Whether Severus helped pointing him in the right direction is irrelevant now." It was only important on a personal level and he would still give Severus the benefit of the doubt.
"He won't," he continued. "I told you, Remus will be fine. He's just worrying to much." Severus had better deliver on his promise, but he supposed that they'd find out soon enough.