Should police attempt to collect the DNA of everyone in the vicinity of a serious crime?

In 2012, Jessica Ridgeway was abducted from a Denver suburb. (She was murdered.) During the search for her, the police voluntarily collected the DNA of about 500 people who made cell phone calls around the time and location of the abduction. Ultimately, Jessica's body was found, and the suspect turned himself in before the DNA was processed. However, the suspect gave his DNA voluntarily, and he would have been caught by his DNA. Is this a proper method of police investigation? Even though people can refuse, does it violate rights?

See: http://www.thedenverchannel.com/news/jessica-ridgeway/suspect-in-jessica-ridgeway-murder-austin-sigg-appears-in-court-thursday