Would Lucius Have Killed Harry?

' “Many people have noticed that it makes no sense for Lucius to attempt to kill Harry for a multitude of reasons, but especially because they are at Hogwarts just outside Dumbledore's office. “Despite Dobby's protective quote, I don't think Lucius intended to kill Harry at all, he intended to kill Dobby.”

What if Lucius Malfoy killed Harry Potter?

So, if Lucius would have killed harry he'd have already destroyed the first horcrux of lord voldemort when voldemort was very weak. Nothing would happened to harry as he would come back from the limbo.

What spell was Lucius using?

In films. In the film adaptation of Harry Potter and the Chamber of Secrets, Lucius Malfoy says "Avada-" at Harry Potter after he unwillingly frees Dobby. Dobby knocks Lucius backwards with magic to protect Harry, and he does not finish the incantation.