Most of the time I can't. When I did I usually had already gotten into their email. Most of my successes are from people with no security on their account.
BUT if you log into the snapchat website you can still get wins. Just request a copy of the data to download and then keep refreshing the page until its done. The person will get an email ONLY when the data request download is finished, so if you stay on the page and get it before they can change their password you can get a record of all of the snaps they've ever saved (not the ones in my eyes only though, but I rarely come across accounts that even use it)
You can also find a script to download all the images and videos quickly once you get the zip file of the data downloaded.