Malfoy Sr's Intent with TMR's Diary (CoS)

[distaiyi]

No: HPFGUIDX 114382

Could it be that Lucius merely wanted something he could pin on the 
Weasleys? "Oh my, my, the Weasleys have really been up to no good! 
Look here what their dear daughter brought into the hallowed halls 
of Hogwarts! Tom Riddel's Diary from 50 years ago!"

Thus deflecting attention from him to Mr. Weasley.

Just a thought... sometimes the most simple answer is the answer.