In the scene where Jeff says they should swing by to see Willard in person it is full sun. When they pull up to his house in the next scene it is dark.
In a common TV movie mistake, the doctor says the victims were incapacitated by a stun gun. Stun guns do not knock out people, they are a pain compliance weapon used to keep an attacker away from you. Holding a stun gun against someone for 3-5 seconds would result in a loss of balance and disorientation but not loss of consciousness. This error is repeated when a girl is knocked out after a less than one second use of the stun gun.
While looking at the crime scene as the first person arriving, Jeff touches all of the doors and surfaces with his bare fingers. He repeats this error outside when checking the power box. As a "retired" detective, he would know that doing so could disturb any fingerprints that may have been present.
The suspect is being interrogated by the police chief and says he wants a lawyer. Regardless of this, Jeff questions him. While he was not an officer, he was acting as an agent of the police. Courts have ruled the Miranda protections apply under these circumstances, so anything the suspect may have said would be inadmissible. Someone with the experience the character was said to have would know this and not make that type of error.