(a) When the writ of habeas corpus is served on the person to whom it is directed, either personally or by being left with any deputy or agent of the person at the place where the prisoner is detained, such person shall, without delay and within 3 days thereafter, produce the body of the prisoner as therein commanded; and shall fully certify in writing and under oath, the true cause or causes of the prisoner's detainer, and a copy of all process under which the prisoner is detained.
(b) The return may be contradicted, and may also be amended.