Needless to say, I can't tell you exactly what I'm trying to imply, but ideally, the clues the forensic scientist gives should help the players find both the key evidence as well as the murder means.
Sometimes it all falls into place nicely; say the murderer used a knife and had food ingredients as their key evidence. Playing the kitchen as a location is a great way to indicate both. Other times, the two will be much harder to indicate in a single clue, and the scientist will need to divide their attention. Let's say the cards picked were a pistol and teddy bear as key evidence. The forensic scientist plays a card indicating the victim was young. That tells you very little about the means used (they may use other cards for that, such as an indication the death was sudden), but it does give a decent hint for the evidence card.
One game I was in the murderer thought they had it dead to rights; there were so many blunt instruments around the table. He had a table leg and wrench, other players had candlesticks, hammers, steel pipes, police batons, a baseball bat etc. however, the key evidence they used was "grass". The forensic gave the location as the park. At that point, most of the table was so focused on him for having one of the few pieces of evidence that could fit, that they got him by process of elimination. That was a little lucky though, as the players could have just as easily seen park and focused on the baseball bat. It's really up to the players to keep an open mind about how the evidence could be interpreted.