It looks like chapter 47 is where Draco tells Harry about Narcissa's death, and I'm not seeing anything about Lucius' being an eyewitness. The chapter seems to imply that Lucius was told, just like everyone else:

"Draco," Harry said, he let all of the hoarseness into his own voice, it would be wrong to sound calm, "I'm sorry, I'm so sorry for asking, but I have to know, how do you know it was Dumble-"

"Dumbledore said he did it, he told Father it was a warning! And Father couldn't testify under Veritaserum because he was an Occlumens, he couldn't even get Dumbledore put on trial, Father's own allies didn't believe him after Dumbledore just denied everything in public, but we know, the Death Eaters know, Father wouldn't have any reason to lie about that, Father would want us to take revenge on the right person, can't you see that Harry?" Draco's voice was wild.