A Man Alone - S1-E4
Corrected entry: Odo becomes the prime suspect in the murder as he, being a shapeshifter, could have got between the cracks of the holodeck door in his liquid form. However, no one realises that even if he were the murderer, the murder weapon, a knife, would not have got through the door cracks with him. Odo wouldn't have needed a weapon anyway, as he can turn his arms into tentacles to strangle the victim.
Correction: Odo could have had the computer replicate a knife quite easily.
Greg Dwyer