After the revelations of the Prophet he had happened upon in the Drawing Room the day before, he had ventured out to seek the information to fill the years he had missed. Whilst the Prophet, naturally, could not provide him with a whole tale and perhaps even an inaccurate story, it provided a basis.
"It would seem not; Bellatrix spent a great portion of time in Azkaban following the first war, alongside Rodolphus. Once she gained her freedom I am sure there were more important considerations," Lucius had found no mention of his own name in regards to the First War, not even a byline of investigation - though he struggled to imagine that the Ministry had never arrived at his doorstep.
The matter of Regulus' brother was a little clearer, with the threads of memory that had led towards the climax of the First War.
"When the Dark Lord fell, your brother was imprisoned in the belief that he had handed the Potters to Him, and that he had murdered his friend Peter Pettigrew," this information was imparted with a harder edge to his voice than before. Regulus' errant older brother had clearly received his just deserts for turning against his family, his blood.
"I remember Peter," he said with a pointed look at Regulus, wondering if he remembered too that Sirius could not possibly have been guilty. Lucius recalled a small, snivelling man, unworthy of their presence but for the wealth of information he held. "Your brother remained a blood traitor, but it would appear that he spent twelve years tucked away before he escaped."
"Your mother must have been so ashamed," Lucius said softly, "though at least one son provided her with the illusion of devoted service." This was not a comment that would endear Regulus to him, but it was true nonetheless. He wasn't quite able to help himself from it.