The site, which lists the UK's most wanted criminals for murder, rape and other crimes, went down after it received more than 208,000 hits in its first few hours of use.
Crimestoppers, a registered charity which designed the site to support current police appeals said it had not expected so many visitors.
The crash would not have happened if it had been properly load-tested, said Daryl Cornelius of security company Spirent Communications. "You design, you test it, then you deploy it and there seems to be a step missing here," he said.
Organizations can avoid a similar fate by testing the physical bandwidth, then the network elements individually and then the entirety of the structure before going live, Cornelius said.
"If I were an e-criminal" he said, "this is one site I would be looking at."www.crimestoppers-uk.org/wanted/