Roger mentions "if the straitjacket fits" about a mentally ill person. In Lethal Weapon 2, Riggs wears and then escapes from a straitjacket for a bet.
When Roger and Martin enter the victims apartment they mention he was a "Conspiracy Theorist". Mel Gibson from the original Lethal Weapon movies starred in a movie about conspiracy theories (Conspiracy Theory) 1997
During the celebrity bus tour the guide specifically mentions Gary Busey. Gary Busey played Mr. Joshua, an antagonist, in the original Lethal Weapon.