The two women were found in a burning car that had been stolen.
Police say those killings are linked to a January 2009 slaying of another Prince George's County nurse mother and daughter who were found shot to death inside their locked home. The girls in each case were students.
An FBI profiler had concluded last year that the two slayings weren't connected. Police say Scott masked his crimes to throw off investigators.
Scott is in custody on federal gun and sex charges.