I know similar questions have been asked before in here, but this is slightly different direction of question.
I'm applying for tenure-track assistant faculty position in my field. But one position requires 5 letter of recommendations. I'm currently working as a post-doc and I know 4 tenured faculty who could write a letter of recommendation for me. But I'm really not sure who should be the 5th one.
Who should I ask to write a letter or recommendation In here, the answerer wrote
Familiarity with your work (research, teaching, service). You want them to provide details for how promising your research is, how you would work with colleagues, how you'd teach and mentor students, and so on.
Familiarity with academic work (tenure-track or tenured professors > other kinds of recommendations). From the perspective of credibility, someone who is familiar with the positions you apply for will be more readily believed when they recommend you. Also, they'll be more likely to mention details that speak directly to the position you'll serve in.
In my current research center, I have a collaborator who is NOT tenured faculty. But he has been full-time research associate in here for 5 yrs, and we researched together and he knows well about my research.
Based on the 2 criteria from other stackexchange answer, can I ask for a letter of recommendation from him? I mean, he is not a faculty, but this application is about tenure-track faculty. Still, could his letter be regarded as a good letter of recommendation?