誰かが逃げるのを見ましたか。

who

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to escape; to run away

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to see; to look; to watch; to view; to observe; to look over; to look on; to assess; to examine; to judge; to look after; to keep an eye on; to take care of; to view (e.g. flowers, movie); to try; to try out; to see that...; to find that...