Same here. Here are the rules for pronunciation in Spanish:
1. When a word without an accent mark ends in a vowel, n, or s, the stress is on the penultimate (second to last) syllable. The majority of Spanish words fall into this category.
Examples: leche, niña, zapatos, comen
2. For words without accent marks that end in any consonant other than n or s, the emphasis is placed on the last syllable.
Examples: hotel, hablar, gratitud, medium
3. If a word’s pronunciation deviates from the above two rules, an accent is placed over the vowel of the syllable where the stress is placed.
Examples: común, lápiz, médico, inglés, ojalá
According to the rules, an accent should be over the first "a" to get the correct pronunciation: "Sántillan". However, many Latino families who have lived in the U.S. for a long time and have become assimilated into American culture often ignore the accent rules, and write their names without the accents, even though they are still pronounced as such. I don't know if Santillan normally writes his name with or without the accent -- I guess we'll find out.