We report on a measurement of the Cabibbo-Kobayashi-Maskawa CP-violating phase γ through a Dalitz analysis of neutral D decays to KS0π-π+ in the processes B∓→D(*)K∓, D*→Dπ0, Dγ. Using a sample of 227×10^6 BB̅ pairs collected by the BABAR detector, we measure the amplitude ratios rB=0.12±0.08±0.03±0.04 and rB*=0.17±0.10±0.03±0.03, the relative strong phases δB=(104±45-21-24+17+16)° and δB*=(-64±41-12+14±15)° between the amplitudes A(B-→D̅ (*)0K-) and A(B-→D(*)0K-), and γ=(70±31-10-11+12+14)°. The first error is statistical, the second is the experimental systematic uncertainty, and the third reflects the Dalitz model uncertainty. The results for the strong and weak phases have a twofold ambiguity.
