NEW : U.S. officials searching databases and communications for possible clues . A plainclothes constable detailed to Parliament was shot in the leg , official says . Canadian army reservist Cpl . Nathan Cirillo killed a soldier at Canada's national war memorial before being gunned down by police outside parliament building. Lawmakers give standing ovation to Parliament official credited with stopping gunman .
NEW : U.S. officials searching databases and communications for possible clues . A plainclothes constable detailed to Parliament was shot in the leg , official says . Canadian army reservist Cpl . Nathan Cirillo was killed at the National War Memorial . Lawmakers give standing ovation to Parliament official credited with stopping gunman .