Part II
Extradition
CHAPTER I
Extradition from Portugal
Section II
Extradition procedure
Article 51
Introductory decision and arrest of the person claimed
4. Should additional information be required, the competent authorities shall be instructed to keep the person claimed under surveillance, unless it is deemed necessary immediately to place that person under arrest on grounds that there are serious reasons for believing that the request will proceed.
EDIT.