  Quantum memory effects can be induced even when the degrees of freedom
associated to the environment are not affected at all during the system
evolution. In this paper, based on a bipartite representation of the
system-environment dynamics, we found the more general interactions that lead
to this class of quantum non-Markovian "casual bystander environments." General
properties of the resulting dynamics are studied with focus on the
system-environment correlations, a collisional measurement-based
representation, and the quantum regression hypothesis. Memory effects are also
characterized through an operational approach, which in turn allows to detect
when the studied properties apply. Single and multipartite qubits dynamics
support and exemplify the developed results.
