。
I spotted him running away from that shop.
Literal
I [topic-は] he [subject-が] that shop [from-から] escape-[go-away-ていく] [nominalizer-の]-[object-を] found.
見つける ('to find, discover, spot') here takes a nominalized perception clause as its object — 'found [him running away].' 逃げて行く ('run away,' combining 逃げる + ていく, moving away from the speaker's perspective). 見つける is used in the perception-of-event sense rather than the literal 'find an object' sense.