On Tuesday, the NOPD arrested Melvin Galle Jr (40) for the attempted murder and armed robbery of Garda Hanrahan on January 27.
Mr Galle’s brother Keith Galle was also arrested but detectives have not named him as a suspect at this time.
New Orleans police are still seeking assistance in locating and identifying the second suspect.
Garda Hanrahan (32), a native of Tipperary, was shot in the legs and lower back while on holiday in New Orleans with his father.
His colleagues in Limerick say he is recovering steadily after surgery, but that he may now face a medical bill of up to $1 million.
An account in the name of Brian Hanrahan has been opened at St Paul’s Garda Credit Union, Bohermanna Road, Cork to help raise funds for travel and medical expenses. The account number is 55322.