A system comprises one or more first electromagnetic coils configured to generate and direct first excitation signals toward a plurality of casings in a wellbore and receive response signals based on the excitation signals. The system also comprises a magnetic field source configured to generate a static magnetic field in a particular casing of the plurality of casings and a magnetometer configured to receive response signals based on the static magnetic field in the particular casing. The system further comprises one or more processors configured to receive a first response signal from the one or more electromagnetic coils, receive a second response signal from the magnetometer, and determine, based on the first response signal and the second response signal, whether a defect exists in the plurality of casings.