What was found
CREW NOTED JUST AFTER TAKEOFF AND IN CRUISE FLT THEY STARTED GETTING A BAD ODOR IN THE CABIN, SO THEY RETURNED TO DEPARTURE FOR MAINTENANCE. THEY LANDED SAFELY BUT DID A EMERGENCY EVAC AC ON TAXIWAY. MAINTENANCE PERFORMED INSPECTIONS OF DUCTING AND SEVERAL COMPARTMENTS. COULD NOT FIND EVIDENCE OF FLUIDS OR ODOR. ISSUED MEL FOR APU. INSPECTED APU COMPARTMENT, ECS COMPARTMENT, ENG COWLING, AND PERFORMED OPS CHECK OF APU. RAI APU IAW MM WORKCARD NR 49-800-05. (K)