Murphy makes a claim to have "cyanide tipped bullets". Even though the sheriff had just released him, Murphy would have been immediately arrested again, since poisoned bullets are illegal anywhere in the U.S. or Canada.
The monster's size varies considerably. In the early parts of the battle on the island its size relative to the humans near it is less than half its size in Loch Ness and later in the fight.
Sheriffs in Canada are not like the law enforcement professionals who hold the same title in the USA. In Ontario, sheriffs typically enforce civil orders, such as evictions and the like.