As a lawyer with many years of criminal law experience as a magistrate, prosecutor and defense lawyer, let me explain BASIC criminal law to folks here so we can put to rest the conspiracy theories.
The Professional Russian posted some really cool videos online. In fact, dozens or more. These videos show him using items that would possibly require special licenses. It also appears that he may deal in weapons. He also blows up a lot of stuff, and shows the world how to do it, with tannerite. Legal, sure, possibly. But WE all must be aware of the fact that this is going to draw extra scrutiny on this guy. I.E. He's on the radar.
I read that his business partner was just killed by a close range shotgun blast to the head. I read that to mean that it was either suicide, or a passion killing from someone wanted him 100% dead. That sounds personal. In criminal investigations, it's probably easy to quickly narrow down the short list of people with motive, means, and opportunity. Someone close in the deceased guys life. Girlfriend, wife, lover, or ... business partner.
Cops need Probable Cause to obtain warrants and conduct searches. Houses, cars, persons...
Probable cause is a level of reasonable belief, based on facts that can be
articulated, that is required to sue a person in civil court or to arrest and
prosecute a person in criminal court. Before a person can be sued or arrested
and prosecuted, the civil plaintiff or police and prosecutor must possess enough
facts that would lead a reasonable person to believe that the claim or charge is
true.
In his case, the totality of the circumstances would easily rise to probable cause. Searching for evidence of murder weapon, unregistered Class III items, illegal explosives, illegal ammo, dealing in firearms without a license....
I don't see anything suspicious with the searches. Think about it. If YOU were the lead detective, where would YOU focus at least some of your investigation. If someone close to you (business partner, family) died with a shotgun blast to the head, you can bet you'd be on the short list of suspects, and you'd likely be subject to a search warrant for your shotguns and shotgun ammo... for instance.
As for the style of the raid, again, if YOU were in charge of planning a search warrant for a probable murder suspect, well armed with serious hardware, you would bring in hand full of teams to safely conduct the search. In the military it's called overwhelming forces to deter resistance. Sending 4 lightly armed officers might result in 4 dead officers and a fleeing suspect.
For his sake, I hope he's cleared of the murder, and I hope he's not been dabbling in illegal weapons.