Tactile telepathy

Tactile telepathy is a special ability that Aro possesses. Aro can see all the thoughts someone has ever had upon physical contact with them. The longer the contact, the more Aro is able to see.

In New Moon, when Bella was in Italy, Aro attempted to read her mind but failed, just as Edward cannot read Bella's mind.

In Breaking Dawn, Aro uses his talent to read Edward's mind and thus saw into every vampire's mind at the current moment.