  We study the asymptotic behavior and the scattering from infinity problem for
the massive Maxwell-Klein-Gordon system in the Lorenz gauge, which were
previously only studied for the massless system. For a general class of initial
data, in particular of nonzero charge, we derive the precise asymptotic
behaviors of the solution, where we get a logarithmic phase correction for the
complex Klein-Gordon field, a combination of interior homogeneous function,
radiation fields to null infinity and an exterior charge part for the gauge
potentials. Moreover, we also derive a formula for charge at infinite time,
which shows that the charge is concentrated at timelike infinity, a phenomenon
drastically different from the massless case. After deriving the notion of the
asymptotic profile, we prove the scattering from infinity by constructing
backward solutions given the scattering data. We show that one can determine
the correct charge contribution using the information at timelike infinity,
which is important for us to obtain solutions not only for the reduced
equations in the Lorenz gauge but also for the original physical system.
