  We show that if $n=7k/i$ with $i \in \{1,2,3\}$ then the cop number of the
generalised Petersen graph $GP(n,k)$ is $4$, with some small previously-known
exceptions. It was previously proved by Ball et al. (2015) that the cop number
of any generalised Petersen graph is at most $4$. The results in this paper
explain all of the known generalised Petersen graphs that actually have cop
number $4$ but were not previously explained by Morris et al. in a recent
preprint, and places them in the context of infinite families. (More precisely,
the preprint by Morris et al. explains all known generalised Petersen graphs
with cop number $4$ and girth $8$, while this paper explains those that have
girth $7$.)
