The probe was earlier reported by the Wall Street Journal.The investigation, and an earlier probe by a NASA watchdog, has cast a shadow over one of NASA's most ambitious endeavors: sending humans back to the moon from U.S. soil for the first time in nearly half a century.In April, NASA bypassed Boeing - an industry juggernaut with deep ties to space travel - and awarded contracts worth a combined $1 billion to Elon Musk's SpaceX, Amazon.com Inc founder Jeff Bezos' Blue Origin, and Leidos Inc affiliate Dynetics to build lunar landing vehicles that can carry astronauts to the moon by 2024. Boeing was removed from the competition, NASA said in April, without explaining why.Two people briefed on a NASA watchdog investigation told Reuters Boeing's removal was over its contact with Loverro.The sources said NASA's Office of Inspector General found that Loverro told Boeing during a blackout period the company's proposal was incomplete and discussed aspects of the bid that were missing.After discussions with Loverro, Boeing officials submitted another version during the blackout period, raising legal concerns among agency procurement staff, one of the people said.