Flashbangs versus destruction of evidence
<p>If setting fire to a crime scene would be considered destruction of evidence and spray painting a crime scene would be considered destruction of evidence why is the use of <a href="https://en.wikipedia.org/wiki/Stun_grenade" rel="nofollow">flashbangs</a> not considered destruction of evidence?</p>

<p>As a pyrotechnic they have the capacity to start a fire. Short of starting a fire they will expel their products of combustion leaving a residue in their target area that could obscure or contaminate trace evidence.</p>

<p>Destruction of evidence always has to be weighed against dealing with an active situation. Taking a surviving victim to a hospital and treating them also destroys evidence; so does putting out an arson fire by knocking out walls. In all cases, there's an emergency situation and dealing with it is more important than preserving evidence. Flashbangs aren't used once the scene is secure, but rather when the need to end an active situation justifies their use. </p>

police evidence