The Legislative Building at the corner of Taft Avenue and Burgos Street was an imposing architectural edifice destroyed during the war. That first day of September 1947, Guerrero rode his car from Lipa Street in Sampaloc to apply for a job as legal adviser, not in Padre Burgos Street but in the Manila City Hall, the temporary office of the Philippine Senate until it moved three years later to the rebuilt and refurbished complex. Having given up his work as first assistant attorney at Gibbs, Gibbs, Chuidian and Quasha law firm, the job he had after he resigned from the Department of Foreign Affairs, he filled up a form stating his name, birth, and the usual personal matters, but there were quite unusual questions which he answered nonetheless. “Are you an habitual gambler of card, cockfighting, etc?” He wrote down “No.” “Are you addicted to any drug or intoxicating liquor?” “No.” “Are you punctual in the payment of your debts?” “Yes.” “Are you related (by blood or by law) to anybody now working in the Senate?” He wrote “Yes.” His second cousin, Efrain Ma. Guerrero, was working in the Senate. On space allotted for references, he only wrote Antonio Zacarias. On that same day, he was sworn in as legal adviser by Zacarias, the Secretary of the Senate.

From the executive branch of government, he would now be working at the legislative branch. As legal adviser, he would advise the secretary on legal matters particularly on bills and resolutions affecting the office and the entire Senate without having to be insulated from politics. Working fulltime at the Senate allowed him to go to Albert, Reyes, Guerrero, Roces law offices for his private legal practice. It was in November when the senatorial elections were held. Guerrero saw Laurel's re-emergence into the political scene when the latter decided to run for senator under the Nacionalista Party. President Roxas, however, persuaded him to get out of the opposition. Roxas did try hard to convince Laurel from participating in the elections until after the issuance of amnesty in late January 1948. Laurel decided not to run while Osias went on with his senatorial ambition.