A criminal complaint says Smith gave Lawson the money to buy the gun last summer along with $100 for completing the transaction. Smith wasn't allowed to have weapons because of a previous burglary conviction.
U.S. District Judge Edmund Sargus on Monday ordered that Lawson remain in jail. Lawson has pleaded not guilty.
His attorney said Tuesday there's nothing in Lawson's history to suggest he's a danger to the community.
Smith could face the death penalty if convicted of the slayings.
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