If you are talking about the murderer Gary Schara (Agawam), he was a suspect right after the murder occurred and was caught through advances in DNA technology, including the use of Parabon snapshot. LE had a court ordered warrant for the collection of his specific DNA, it was not a voluntary sweep. (source:
Lisa Ziegert case: Gary Schara pleads guilty in 1992 Agawam murder)
Also I want to point out that though a DNA sweep was done in Truro, it did not solve that murder either. The suspect, the man eventually convicted of the crime, had already submitted a DNA sample when questioned by police prior to the sweep. Due to crime lab backlogs, they just hadn't matched his sample to the one at the crime scene yet.
Here is data on how well DNA dragnet work solving cases:
And contrary to the claims of law enforcement, DNA dragnets do not have an impressive success rate in catching criminals. The Baltimore Sun recently reported on a study by researchers at the University of Nebraska that focused on eighteen DNA dragnet cases. “Only one — which focused on just 25 nursing home employees — successfully identified the suspect,” the paper reported. A recent ACLU report, according to USA Today, found similarly low levels of success. “More than 7,000 people have been tested in DNA dragnets nationwide since 1995,” the paper noted, but “only one has identified a suspect.”
Source:
DNA Dragnets
Finally, a major reason LE should be reluctant to use "voluntary" sweeps is because what they do with the DNA samples from non-suspects is a serious legal question. Some LE departments were promising to destroy DNA samples from non-suspects but were instead entering them into databases for comparisons to other unsolved crimes.
Plenty of investigative and legal strategies that were once considered okay are now restricted in use to last resort situations because of their tenuous constitutional status. In my opinion, if you read the comments of both LE and prosecution in the Delphi case, they don't believe they are in that last resort area at this time. For the evolving legal status of dragnets, read more here:
DNA Dragnet