iPhones are extremely difficult to open without the password. Apple does not provide assistance. There are some ways to get into it, but is very very difficult.
LE can get tons of location based info through Google. Google has 3 separate mechanisms that track phones & in fact, some level of analysis may even show what other phones were near him during the day and leading up to the crash. However, unlocking his phone to find snapchat and/or other messaging apps may not ever be possible or could take considerable time.