+ e - e + - + W - W - ,  - e e,  ) s ( (u) + K + - (770) (a) + e - e + - + W - W - ,  - e e,  (u) ) s ( + - + K (892) * K (b) 5 Three-prong decays of the τ are selected from candidate τ $^{+}$τ − pair events as follows. We use events where the number of charged tracks is four and the sum of their charges is zero; the transverse momentum of each track in the laboratory frame is required to be larger than 0.1 GeV/ c , and the tracks should extrapolate back to the interaction point within ± 5 cm along the beam direction and ± 1 cm in the transverse plane. The sum of the reconstructed tector is a large-solid-angle magnetic spectrometer that consists of a silicon vertex detector (SVD), a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters (ACC), a barrel-like arrangement of time-of-flight scintillation counters (TOF), and an electromagnetic calorimeter (ECL) comprised of CsI(Tl) crystals located inside a su- perconducting solenoid coil that provides a 1.5 T magnetic field. An iron flux return located outside the coil (KLM) is instrumented to detect K 0 L mesons and to identify muons. The detector is described in detail elsewhere [14]. SELECTION OF EVENTS FIG. 1: A schematic view of e $^{+}$e − → τ $^{+}$τ − in the center-of-mass system, where one τ ( τ $^{+}$) decays to the signal mode ( τ + → K $^{+}$π $^{−}$π $^{+}$ν$_{τ}$ ) and the other τ ( τ $^{−}$) decays to a leptonic mode ( τ − → e $^{−}$ν$_{τ}$ ν$_{e}$ or τ − → µ $^{−}$ν$_{τ}$ ν$_{µ}$ ). Each figure shows one of two possible intermediate resonant states in the signal mode.