No, police officers should not be allowed to work on cases in which they are personally involved because it creates a clear conflict of interest. While television cop shows often play the involvement of an investigating officer for drama, in real life, any personal involvement would and should disqualify an officer from working on a case. In some cases, the officer may actually be a suspect or a witness; for instance, if the officer is the girlfriend of someone involved in a drug ring. In other occasions, restricting involvement would protect the officer as much as the case itself. If an officer worked on the murder of her child, for instance, that could potentially traumatize the officer and ruin her career. In the long run, the involvement of an officer with personal ties to the case could lead to a poor outcome in court, leaving the investigation open to accusations or bias which would put any evidence or testimony under suspicion.
The police department is one section of the justice department. Just as judges and prosecutors are not allowed to work on cases that involve family members, police officers should not be able to work on cases in which they are personally involved. Police officers should actually be ok with this rule as it could come up in court to work against a family member of theirs if the jury, etc thinks there was a bias involved. Plus, police officers would be more stressed when the work involves their family that mistakes could be made. It's best if they are kept out of investigations,etc and just be notified when new details arise like any other citizen.
No, police offers should not be allowed to work on cases in which they are personally involved because it will create a bias. If a police officer wants to help his or her colleague, he or she may lie to get them exonerated, regardless of whether the crime was committed.
Police officers should recuse themselves from cases in which they are personally involved. Failing this, officers should be removed from working on these cases. It is a clear conflict of interest, and it clouds people's judgements. This is even true for the most dedicated professional police officer. It also creates other conflicts, such as the possibility an officer will seek revenge on an enemy through an arrest.