Why didn't Karkaroff out Lucius Malfoy?

[Tom Wall <thomasmwall@yahoo.com>]

No: HPFGUIDX 53113

Hey all,

I've been thinking about the 
whole trial bit post the first 
fall of Lord Voldemort, and I 
haven't been able to connect 
something to my own liking, so
I figured I'd see what y'all 
think.

"Father actually considered sending me to Durmstrang rather than 
Hogwarts, you know. He knows the headmaster, you see."
(GoF, US hardcover, Ch.11, 165)

"Karkaroff got released?" <snip>
"He did a deal with the Ministry of Magic," said Sirius bitterly. "He 
said he'd seen the error of his ways, and then he named names... he 
put a load of other people into Azkaban in his place... He's not very 
popular in there, I can tell you."
(GoF, US hardcover, Ch.19, 332)

And then we have Karkaroff's naming of the names in Ch.30. He gives 
the Council Antonin Dolohov, Evan Rosier, Travers, Mulciber, Augustus 
Rookwood, and Snape.

But, despite the fact that Karkaroff points out that only Lord 
Voldemort knew the names of all of the Death Eaters (Ch.30, 588), we 
also know that Lucius Malfoy and Karkaroff know each other.

And since they knew each other I figure that that's a) because they 
attended Hogwarts together, b) because they were both Death Eaters 
together, or c) both.

I find it hard to believe that Karkaroff wouldn't know that Lucius 
was a Death Eater. I mean, sure, it's possible, but given that they 
know each other, I still find it hard to believe.

So, why wouldn't Karkaroff out Malfoy to save his own neck?

-Tom