Because the TONE and STYLE of his conversations and communications changed.
I vote that he was abducted...for whatever reason. Leaving the dog unattended almost completely rules out suicide (I know a few things about some suicides). Additionally, leaving his ID tells me leaving wasn't his idea. From the sounds of it, he was pretty close to his family. Even if he wanted to complete suicide, he would have wanted his family to know.
Hit job.
We can’t know what all could have happened to him unless we know what all he could get his hands on.
Who would have wanted this hard-working successful man dead and why?
No mention of a girlfriend. No pictures of women on his Facebook except mom and sister.
Obama supporter who published papers on how blacks are short-changed on healthcare.
Another little tidbit I found, “Cunningham, a commander in the United States Public Health Service and epidemiologist with the CDC, was last heard from on Feb. 12 after leaving work early and filing for a two-week sick leave. “He sounded not like himself,” Tiara Cunningham, the commander’s sister told The New York Times.” I don’t believe he was sick, I think he was scared. Even if you feel sick you don’t typically ask for 2 weeks off.
http://miami.cbslocal.com/2018/02/26/cdc-researcher-vanishes-sick-missing-person/
I watched an interview with his neighbor and the lady said they had exchanged phone numbers a while back when he had accidentally left his garage door open. She said that her husband had a strange interaction with Cunningham on the day he disappeared. Her husband said Cunningham told him to have his wife take his phone number out of her phone. (She said she hadn’t put it in her phone, just had it on a piece of paper.) The first thing I thought of was he knew someone might go through his phone and he didn’t want her to be linked to him.