bob buehner says there could be a simple explanation for that. he spoke to "dateline" before he retired as a d.a. >> frankly, i'm thinking about the same thing. i've got lots of stuff on that hard drive. yeah, i probably would like to get rid of it. i don't have any need for it. >> reporter: and, after all, why would ray drive 60 miles to dump a hard drive in the river when he could dispose of it closer to home? but if ray didn't remove the hard drive, then someone else apparently did. maybe, investigators speculated, there was something incriminating on it. you'd like to know what is on that hard drive. >> we think there was information on there that would lead us to one of the theories, a reason why somebody would want him dead, why he would jump in in the river, or why he wanted to leave. >> reporter: three theories. that's what investigators were left with to explain what happened to ray gricar. does your department lean in any particular direction? >> no, actually, we don't. and it's hard because we all have our personal thoughts on the case