Inquiring into the costs of inquiries

The bill for the government inquiries into events in the Troubles has topped £200m. Interestingly:

“Two of those inquiries – concerning collusion in the murders of Mrs Nelson and Robert Hamill – have already cost more than the full inquiry into the racist murder of black teenager Stephen Lawrence.

The Lawrence Inquiry was considered thorough and produced a highly significant report. The scale of Bloody Sunday sets it apart but why are the other local inquiries unable to achieve the same standards as the Lawrence inquiry for similar costs?