The U.S. Olympic Committee didn’t intervene in USA Gymnastics’ handling of sexual-abuse allegations against longtime national-team doctor Larry Nassar in 2015, even after USA Gymnastics’ then-president told two top USOC executives that an internal investigation had uncovered possible criminal behavior by the doctor against Olympic athletes.

The communications—a July 2015 phone call and a September 2015 email described to The Wall Street Journal by people familiar with the matter—shed new light on the Olympic Committee’s knowledge...