Afonti,
If he arrived after 1906 and naturalized after 1912, you would expect to see notations on his manifest of the "Certificate of Arrival" number (not naturalization certificate) and date of issue. This was due to procedures implemented effective 1912 which required a petitioner for naturalization to prove that he entered the US legally.
I suggest you begin by placing an order with the National Archives using the information you have available and see what turns up. NARA responds quickly, often within a week, and will not charge you if they do not locate a record. The only downside to NARA is that, for most of the US, they only hold naturalization records from the federal courts and not from state or county courts. Still, it is definitely worth a shot.
To place a document order, start here
https://eservices.archives.gov/orderonl ... chives.gov and go ahead and create an account on the right. Next, click "Order Reproductions" and then "Immigration & Naturalization Records"
When completing the order form, you may encounter fields which demand you enter something even though you don't have the information available; just put X's or 9's in those fields and continue.
Note: if they do have the records, you are going to want to request the "Certified Paper Copy" which will cost you a total of $22.50 (assuming this is about jus sanguinis citizenship).
For all naturalizations after September 27, 1906, the most reliable sorce of records - no matter what level court may have been involved - is the United States Citizenship & Immigration Service ("USCIS"). The negative factor is USCIS is more costly and orders of magnitude slower to respond than other sources. Start here and request an "Index Search" (
http://www.uscis.gov/portal/site/uscis/ ... 18190aRCRD ). If the Index Search turns up a citizenship file ("C" File), then you would follow up with a "Records Request" to obtain the actual documents.
