Q:

Can I use the phrase, “open and shut” for other subjects than legal cases?

There was the following passage in New York Times (April 28) under the title,
“In Baltimore, we’re all Freddie Gray.”:

“We’ve watched as Mayor Stephanie Rawlings-Blake, in conjunction with
  Police Commissioner Anthony W. Batts, spent over a week investigating
  what appears to be an open-and-shut case. I’d like to think that if I
  broke a person’s neck for no reason, I’d be charged in minutes. But
  the system — even when it’s run by a black mayor and a majority of the
  City Council is black — protects the police, no matter how blatant and
  brutal they are.

As I am unfamiliar with the expression,“open and shut,” I searched the meaning on Google, and found the following definition by the Free Dictionary among several sources:

Open and shut - If a legal case or problem is open and shut, the facts
  are very clear and it is easy to make a decision or find a solution

Is the usage of idiom, “open and shut” limited to legal matters? If it came from the instantaneous action of opening and shutting something like a box or drawer, why can’t we use it on anything, questions (e.g. simple calculation) or problems that are manifest or easy to solve other than legal cases? 

A:

An expression generally , but not exclusively, used referring to legal matters :
Open-and-shut case:

a legal case or other matter that is easy to decide or solve. (Oxford Learner's)

Open-and-shut case

a simple and straightforward situation without complications. (Often said of criminal cases where the evidence is convincing.)

The murder trial was an open-and-shut case. The defendant was caught with the murder weapon. Bob's death was an open-and-shut case of suicide. He left a suicide note.

The Free Dictionary

Chevrolet presents an open-and-shut case   against the van you are using. ( From LIFE 12 giu 1970)

An open and shut case?: Title of an article with political content.

An Open-and-Shut Case? Recent Insights into the Activation of EGF/ErbB Receptors
. A scientific/medical extract.

