Every time you use an idea that is not your own or information that is not common knowledge in your writing you have to site the source directly in your text.
1st use of source:
Ross and Myers (2009) argue that traffic stops deserve more critical attention because of the wide range of privacy rights issues and officer safety issues they can pose.
2nd use of source:
Issues surrounding traffic stops require careful Fourth Amendment analysis (Ross & Myers, 2009).
Ross and Myers posit that “the touchstone of the Fourth Amendment is reasonableness” and that it has been considered reasonable for police to remove any or all occupants from a vehicle during a traffic stop at their discretion (2009, p. 470).
Source: Lee, C. (2011, January 27). Writing in-text citations in APA style [Blog post]. Retrieved from http://blog.apastyle.org/apastyle/2011/01/writing-in-text-citations-in-apa-style.html