varNa question

[Robert, Eric]

Dear list members,

I've got to make a small work about the system of varNa in India. While
trying to collect some data, I found 2 sources with 2 very different
statements.
One says that, for a given crime, a shudra was punished more heavily than a
vaishhya, himself more than a kshhatrya (with a reference to Manu smRti).
The second source says the opposite, that the punishment was in relation
with the responsability, i.e., a vaishhya would receive a punishment twice
as heavy as a shudra, and a kshhatrya twice as heavy as a vaishhya.

Now, in Mahabharata,the eldest brother among pandavas, Yudhistir was asked
to do a justice for a crime which involved four people from four different
varNa. He gave the severest punishment possible to the one who was from
BhramaN varNa since he was the most knowledgeble among the four to know what
is right and wrong. Whereas he gave the least punishment to the person from
shudra varNa because he was uneducated and was least likely to plan for that
crime.

I would like to know which source is right (maybe both?) and possibly get
more textual references.
In advance thank you.

Dr. Eric Robert