There is no definitive proof that Lenk planted the key in Avery's trailer. There is, however, concrete proof that Steven Avery handled that key. The rebuttal to Avery's DNA being found on the key contains some major logistical holes. The most prevalent hole is in regards to the alleged methods used by Lenk and/or Colburn. For example, if Lenk and/or Colburn went through the trouble (e.g., going through two locked doors at the Clerk's Office) of obtaining Avery's blood and placing it inside Halbach's vehicle, why not simply place a minute amount of blood on the key? Why deposit Avery's blood inside Halbach's vehicle, yet deposit Avery's Touch DNA on the key to Halbach's vehicle?
Avery supporters are basically postulating that instead of framing Avery in one fell swoop, Lenk and/or Colburn went about this frame-up in a random manner. IMO, that narrative is absurd and speaks to the levels that supporters will go to bang square pegs into round holes. This hodge podge thought process only adds to the complexity of this frame-up. In other words, why would Lenk and Colburn purposely make this plan more complicated than it needs to be?