We present the results of near-infrared imaging and spectroscopic observations of the young core-collapse supernova remnant (SNR) G11.2-0.3. In the [Fe II] 1.644 μm image, we first discover long, clumpy [Fe II] filaments within the radio shell of the SNR, together with some faint, knotty features in the interior of the remnant. The filaments are thick and roughly symmetric with respect to the northeast-southwest elongation axis of the central pulsar wind nebula. We have detected several [Fe II] lines and a H I Brγ line toward the peak position of the bright southeastern [Fe II] filament. The derived extinction is large (AV = 13 mag), and it is the brightest [Fe II] 1.644 μm filament detected toward SNRs to date. By analyzing two [Fe II] 1.644 μm images obtained 2.2 yr apart, we detect a proper motion corresponding to an expansion rate of 0.035'' ± 0.013'' yr-1 (830 ± 310 km s-1). In addition to the [Fe II] features, we also discover two small H2 2.122 μm filaments. One is bright and along the southeastern boundary of the radio shell, while the other is faint and just outside its northeastern boundary. We have detected the H2 (2-1) S(3) line toward the former filament and derive an excitation temperature of 2100 K. We suggest that the H2 filaments are dense clumps in a presupernova circumstellar wind swept up by the SNR shock, while the [Fe II] filaments are probably composed of both shocked wind material and shocked supernova (SN) ejecta. The distribution of [Fe II] filaments may indicate that the SN explosion in G11.2-0.3 was asymmetric, as in Cassiopeia A. Our results support the suggestion that G11.2-0.3 is a remnant of a SN IIL/b interacting with a dense red supergiant wind.
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