The resonant substructures of $\Dz \to \fourpi \, $ and $\Dz \to \KKpipi \, $ decays are studied using data collected by the CLEO detector. Amplitude analyses are performed using a data driven regularization procedure to limit the model complexity. For the $\Dz \to \fourpi \, $ decay the prominent contributions are the decay modes $\Dz \to a_{1}(1260)^{+} \, \pi^{-}$, $\Dz \to \sigma \, f_0(1370)$ and $\Dz \to \rho(770)^{0} \, \rho(770)^{0}$. The broad resonances $a_1(1260)^+$, $\pi(1300)^+$ and $a_1(1640)^+$ are studied in detail, including quasi-model-independent parametrizations of their lineshapes.

The amplitude analysis of $\Dz \to \KKpipi \, $ decays uses a significantly improved formalism with respect to previous analyses of the decay. The largest contributions to the decay are found to be the decay modes $\Dz \to \phi(1020) \rho(770)^{0}$, $\Dz \to K_1(1270)^+ K^-$ and $\Dz \to K(1400)^+ K^-$. A search for \CP asymmetries at both global and amplitude component level yield no evidence for \CP violation in either decay mode.\\
The work presented here is published in Ref.~\cite{dArgent2017}.